Electric current : An electric current is defined as the amount of charge flowing through any cross-section of a conductor per unit time, I = . Electric current is a scalar quantity.  Electric current in terms of number of electrons (n) in a conductor, I = , e = charge on an electron = –1.6 × 10–19 C.  In a metallic wire or conductor, the flow of electric current is due to the flow of electrons from one end to the other end of the wire.  Charge carrier in a metallic wire are conduction elements.  6.25 × 1018 electrons make one coulomb of charge.  S.I. unit of electric current is ampere (A).  Ampere (A) : Electric current through a conductor is said to be 1 ampere if one coulomb charge flows through any cross-section of the conductor in one second.  Ammeter is used to measure electric current.  Ammeter is always connected in series in an electric circuit.  Electric potential is defined as work done per unit charge. V =  Electric potential is a scalar quantity.  Electric potential difference is defined as the work done in moving a unit positive charge from one point to another point. dV =  SI unit of electric potential is volt (V).  Voltmeter is used to measure the potential difference between two points in an electric circuit.  Voltmeter is always connected in parallel in an electric circuit.  Ohm's Law : This law states that, "the electric current flowing in a conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions of the conductor remain the same".  Resistance (R) : Resistance of a conductor is the ability of the conductor to oppose the flow of charge through it.  Unit of resistance is ohm.  1 Ohm : Resistance of a conductor is said to be 1 ohm if a potential difference of 1 volt across the ends of the conductor produces a current of 1 ampere through it. Resistor is a component (say a metallic wire) in an electric circuit which offers resistance to the flow of electrons constituting the electric current in the electric circuit.  Law of Resistance : (i) Resistance of a conductor depends upon the nature of the material of the conductor. (ii) Resistance of a conductor is directly proportional to the length of the conductor. (iii) Resistance of a conductor is inversely proportional to the each of cross-section of the conductor. (iv) Resistance of metallic conductor increases with the increase of temperature and decreases with the decrease of the temperature.  R =  Resistivity or Specific Resistance () : Resistivity is defined as the resistance of the conductor of unit length and unit area of cross-section.  Unit of Resistivity : In CGS system, unit if resistivity is ohm-cm. In SI system, unit of resistivity is ohm-metre.  Two or more resistors are said to be connected in series if same amount of current flows through these resistors.  The effective resistance of series combination of resistors is the algebraic sum of the individual resistances of the resistors in the combination.  An electric bulb or a heater or a metallic wire acts as a resistor.  If one of the electric bulbs connected in a series is fused, then no electric bulb will glow inspite of the fact that the combination is connected with a source of electric current.  Two or more resistors are said to be connected in parallel if the potential difference across each resistor is equal to the applied potential difference across the combination of the resistors.  The effective resistance of the resistors connected in parallel is less than the minimum resistance of a resistor in the combination.  Resistors are connected in series if the resistance of the electric circuit is to be increased.  Resistors are connected in parallel if the resistance of the electric circuit is to be decreased.  Joule's Law of Heating : The amount of heat produced in a conductor is (i) Directly proportional to the square of the electric current flowing through it. (ii) Directly proportional to the resistance of the conductor. (iii) Directly proportional to the time for which the electric current flows through the conductor. H = I2Rt (joule)  Electric fuse is a safety device used to save the electric appliances from burning.  Electric fuse is a wire made of a material having low melting point.  Electric fuse wire is made of copper or tin-lead alloy.  Electric energy : The work done by a source of electricity to maintain a current in an electric circuit is known as electric energy. E = VIt  Electric power : Electric power is defined as the amount of electric work done in one second. P = VI = I2R = V2 / R  SI unit of power is watt.  Practical unit of power is horse power (h.p.) 1 h.p. = 746 W  Electric energy = Electric power × time  Commercial unit of Energy : kilowatt-hour (kWh)  1 kWh = 3.6 × 106 J

Electric current : An electric current is defined as the amount of charge flowing through any cross-section of a conductor per unit time, I = . Electric current is a scalar quantity.  Electric current in terms of number of electrons (n) in a conductor, I = , e = charge on an electron = –1.6 × 10–19 C.  In a metallic wire or conductor, the flow of electric current is due to the flow of electrons from one end to the other end of the wire.  Charge carrier in a metallic wire are conduction elements.  6.25 × 1018 electrons make one coulomb of charge.  S.I. unit of electric current is ampere (A).  Ampere (A) : Electric current through a conductor is said to be 1 ampere if one coulomb charge flows through any cross-section of the conductor in one second.  Ammeter is used to measure electric current.  Ammeter is always connected in series in an electric circuit.  Electric potential is defined as work done per unit charge. V =  Electric potential is a scalar quantity.  Electric potential difference is defined as the work done in moving a unit positive charge from one point to another point. dV =  SI unit of electric potential is volt (V).  Voltmeter is used to measure the potential difference between two points in an electric circuit.  Voltmeter is always connected in parallel in an electric circuit.  Ohm's Law : This law states that, "the electric current flowing in a conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions of the conductor remain the same".  Resistance (R) : Resistance of a conductor is the ability of the conductor to oppose the flow of charge through it.  Unit of resistance is ohm.  1 Ohm : Resistance of a conductor is said to be 1 ohm if a potential difference of 1 volt across the ends of the conductor produces a current of 1 ampere through it. Resistor is a component (say a metallic wire) in an electric circuit which offers resistance to the flow of electrons constituting the electric current in the electric circuit.  Law of Resistance : (i) Resistance of a conductor depends upon the nature of the material of the conductor. (ii) Resistance of a conductor is directly proportional to the length of the conductor. (iii) Resistance of a conductor is inversely proportional to the each of cross-section of the conductor. (iv) Resistance of metallic conductor increases with the increase of temperature and decreases with the decrease of the temperature.  R =  Resistivity or Specific Resistance () : Resistivity is defined as the resistance of the conductor of unit length and unit area of cross-section.  Unit of Resistivity : In CGS system, unit if resistivity is ohm-cm. In SI system, unit of resistivity is ohm-metre.  Two or more resistors are said to be connected in series if same amount of current flows through these resistors.  The effective resistance of series combination of resistors is the algebraic sum of the individual resistances of the resistors in the combination.  An electric bulb or a heater or a metallic wire acts as a resistor.  If one of the electric bulbs connected in a series is fused, then no electric bulb will glow inspite of the fact that the combination is connected with a source of electric current.  Two or more resistors are said to be connected in parallel if the potential difference across each resistor is equal to the applied potential difference across the combination of the resistors.  The effective resistance of the resistors connected in parallel is less than the minimum resistance of a resistor in the combination.  Resistors are connected in series if the resistance of the electric circuit is to be increased.  Resistors are connected in parallel if the resistance of the electric circuit is to be decreased.  Joule's Law of Heating : The amount of heat produced in a conductor is (i) Directly proportional to the square of the electric current flowing through it. (ii) Directly proportional to the resistance of the conductor. (iii) Directly proportional to the time for which the electric current flows through the conductor. H = I2Rt (joule)  Electric fuse is a safety device used to save the electric appliances from burning.  Electric fuse is a wire made of a material having low melting point.  Electric fuse wire is made of copper or tin-lead alloy.  Electric energy : The work done by a source of electricity to maintain a current in an electric circuit is known as electric energy. E = VIt  Electric power : Electric power is defined as the amount of electric work done in one second. P = VI = I2R = V2 / R  SI unit of power is watt.  Practical unit of power is horse power (h.p.) 1 h.p. = 746 W  Electric energy = Electric power × time  Commercial unit of Energy : kilowatt-hour (kWh)  1 kWh = 3.6 × 106 J

Electric current : An electric current is defined as the amount of charge flowing through any cross-section of a conductor per unit time, I = . Electric current is a scalar quantity.  Electric current in terms of number of electrons (n) in a conductor, I = , e = charge on an electron = –1.6 × 10–19 C.  In a metallic wire or conductor, the flow of electric current is due to the flow of electrons from one end to the other end of the wire.  Charge carrier in a metallic wire are conduction elements.  6.25 × 1018 electrons make one coulomb of charge.  S.I. unit of electric current is ampere (A).  Ampere (A) : Electric current through a conductor is said to be 1 ampere if one coulomb charge flows through any cross-section of the conductor in one second.  Ammeter is used to measure electric current.  Ammeter is always connected in series in an electric circuit.  Electric potential is defined as work done per unit charge. V =  Electric potential is a scalar quantity.  Electric potential difference is defined as the work done in moving a unit positive charge from one point to another point. dV =  SI unit of electric potential is volt (V).  Voltmeter is used to measure the potential difference between two points in an electric circuit.  Voltmeter is always connected in parallel in an electric circuit.  Ohm's Law : This law states that, "the electric current flowing in a conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions of the conductor remain the same".  Resistance (R) : Resistance of a conductor is the ability of the conductor to oppose the flow of charge through it.  Unit of resistance is ohm.  1 Ohm : Resistance of a conductor is said to be 1 ohm if a potential difference of 1 volt across the ends of the conductor produces a current of 1 ampere through it. Resistor is a component (say a metallic wire) in an electric circuit which offers resistance to the flow of electrons constituting the electric current in the electric circuit.  Law of Resistance : (i) Resistance of a conductor depends upon the nature of the material of the conductor. (ii) Resistance of a conductor is directly proportional to the length of the conductor. (iii) Resistance of a conductor is inversely proportional to the each of cross-section of the conductor. (iv) Resistance of metallic conductor increases with the increase of temperature and decreases with the decrease of the temperature.  R =  Resistivity or Specific Resistance () : Resistivity is defined as the resistance of the conductor of unit length and unit area of cross-section.  Unit of Resistivity : In CGS system, unit if resistivity is ohm-cm. In SI system, unit of resistivity is ohm-metre.  Two or more resistors are said to be connected in series if same amount of current flows through these resistors.  The effective resistance of series combination of resistors is the algebraic sum of the individual resistances of the resistors in the combination.  An electric bulb or a heater or a metallic wire acts as a resistor.  If one of the electric bulbs connected in a series is fused, then no electric bulb will glow inspite of the fact that the combination is connected with a source of electric current.  Two or more resistors are said to be connected in parallel if the potential difference across each resistor is equal to the applied potential difference across the combination of the resistors.  The effective resistance of the resistors connected in parallel is less than the minimum resistance of a resistor in the combination.  Resistors are connected in series if the resistance of the electric circuit is to be increased.  Resistors are connected in parallel if the resistance of the electric circuit is to be decreased.  Joule's Law of Heating : The amount of heat produced in a conductor is (i) Directly proportional to the square of the electric current flowing through it. (ii) Directly proportional to the resistance of the conductor. (iii) Directly proportional to the time for which the electric current flows through the conductor. H = I2Rt (joule)  Electric fuse is a safety device used to save the electric appliances from burning.  Electric fuse is a wire made of a material having low melting point.  Electric fuse wire is made of copper or tin-lead alloy.  Electric energy : The work done by a source of electricity to maintain a current in an electric circuit is known as electric energy. E = VIt  Electric power : Electric power is defined as the amount of electric work done in one second. P = VI = I2R = V2 / R  SI unit of power is watt.  Practical unit of power is horse power (h.p.) 1 h.p. = 746 W  Electric energy = Electric power × time  Commercial unit of Energy : kilowatt-hour (kWh)  1 kWh = 3.6 × 106 J

 Light is a form of energy which produces the sensation of sight.  Speed of light in vacuum / air = 3 × 108 ms–1  Ray of light : A line drawn in the direction of propagation of light is called ray of light.  Beam of light : A group of parallel rays light emitted by a source of light is called beam of light.  Reflection of light : The phenomenon of returning of light in the same medium after striking a surface is called reflection of light.  Laws of reflection : The reflection of light from a surface obeys certain laws called laws of reflection. (i) incident angle is equal to reflected angle i.e. i = r. (ii) Incident ray, reflected ray and normal to the reflecting surface at the point on incident lie in the same plane.  Concave mirror : concave mirror is a part of a hollow sphere whose outer part is silvered and the inner part is reflecting surface.  Convex mirror : convex mirror is a part of a hollow sphere whose outer part is reflecting surface and inner part is silvered.  Centre of curvature : The centre of a hollow sphere of which the spherical mirror forms a part is called centre of curvature. It is denoted by C  Radius of curvature : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature. It is denoted by R  Pole : The mid point of a spherical mirror is called its pole. It is denoted by P  Aperture: The part of spherical mirror exposed to the incident light is called the aperture of the mirror.  Principal Axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror and extend on either side is called principal axis of the spherical mirror.  Principal Focus : A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appears to meet after reflection from the spherical mirror is called principal focus. It is denoted by F.  Focal Plane : A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of the spherical mirror is called focal plane of the spherical mirror.  Focal length (f): The distance between the pole (P) and the principal focus (F) of a spherical mirror is called the focal length of the spherical mirror.  f = , Where R is the radius of the curvature of the mirror.  Focal length and radius of curvature of a concave mirror are negative.  Focal length and radius of curvature of a convex mirror are positive.  Sign Conventions for reflection by spherical mirrors (1) All distance are measured from the pole of a spherical mirror. (2) Distance measured in the direction of incident light are taken as positive. Distance measured in the direction opposite to that of the incident light are taken negative. (3) The upward distance perpendicular to the principal axis are taken as positive, while the downward distance perpendicular to the principal axis are taken as negative.  Radius of curvature plane mirror =  ( infinite)  Focal length of a plane mirror =   Mirror Formula : The relation between u, v, and focal length (f) of a spherical mirror is known as mirror formula. That is  Linear magnification : Linear magnification produced by a mirror is defined as the ratio of the size ( or height) of the image to the size of the object . It is denoted by m. That is  Power of mirror (P) = =  Linear magnification produced by a plane mirror = + 1.  Refraction of light: The bending of light rays when they pass obsessively from one medium to the other medium is called refraction of light .  A transparent medium through which light travels fast is known as optically rarer medium.  A transparent medium through which light travels slow is known as optically denser medium.  Laws of refraction (i) The incident ray, the refracted ray and the normal to the surface separating two media all lie in the same plane. (ii) The ratio of the sine of the incident angle (i) to the sine of the refracted angle (r) is constant i.e. sin i/ sin r = constant This constant is known as the refractive index of second medium w.r.t the first medium.  Absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v) i.e. n = c / v  Relative refractive index of medium. 2 w.r.t. the medium 1 is defined as the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). i.e. n21= v2 / v1

 Light is a form of energy which produces the sensation of sight.  Speed of light in vacuum / air = 3 × 108 ms–1  Ray of light : A line drawn in the direction of propagation of light is called ray of light.  Beam of light : A group of parallel rays light emitted by a source of light is called beam of light.  Reflection of light : The phenomenon of returning of light in the same medium after striking a surface is called reflection of light.  Laws of reflection : The reflection of light from a surface obeys certain laws called laws of reflection. (i) incident angle is equal to reflected angle i.e. i = r. (ii) Incident ray, reflected ray and normal to the reflecting surface at the point on incident lie in the same plane.  Concave mirror : concave mirror is a part of a hollow sphere whose outer part is silvered and the inner part is reflecting surface.  Convex mirror : convex mirror is a part of a hollow sphere whose outer part is reflecting surface and inner part is silvered.  Centre of curvature : The centre of a hollow sphere of which the spherical mirror forms a part is called centre of curvature. It is denoted by C  Radius of curvature : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature. It is denoted by R  Pole : The mid point of a spherical mirror is called its pole. It is denoted by P  Aperture: The part of spherical mirror exposed to the incident light is called the aperture of the mirror.  Principal Axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror and extend on either side is called principal axis of the spherical mirror.  Principal Focus : A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appears to meet after reflection from the spherical mirror is called principal focus. It is denoted by F.  Focal Plane : A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of the spherical mirror is called focal plane of the spherical mirror.  Focal length (f): The distance between the pole (P) and the principal focus (F) of a spherical mirror is called the focal length of the spherical mirror.  f = , Where R is the radius of the curvature of the mirror.  Focal length and radius of curvature of a concave mirror are negative.  Focal length and radius of curvature of a convex mirror are positive.  Sign Conventions for reflection by spherical mirrors (1) All distance are measured from the pole of a spherical mirror. (2) Distance measured in the direction of incident light are taken as positive. Distance measured in the direction opposite to that of the incident light are taken negative. (3) The upward distance perpendicular to the principal axis are taken as positive, while the downward distance perpendicular to the principal axis are taken as negative.  Radius of curvature plane mirror =  ( infinite)  Focal length of a plane mirror =   Mirror Formula : The relation between u, v, and focal length (f) of a spherical mirror is known as mirror formula. That is  Linear magnification : Linear magnification produced by a mirror is defined as the ratio of the size ( or height) of the image to the size of the object . It is denoted by m. That is  Power of mirror (P) = =  Linear magnification produced by a plane mirror = + 1.  Refraction of light: The bending of light rays when they pass obsessively from one medium to the other medium is called refraction of light .  A transparent medium through which light travels fast is known as optically rarer medium.  A transparent medium through which light travels slow is known as optically denser medium.  Laws of refraction (i) The incident ray, the refracted ray and the normal to the surface separating two media all lie in the same plane. (ii) The ratio of the sine of the incident angle (i) to the sine of the refracted angle (r) is constant i.e. sin i/ sin r = constant This constant is known as the refractive index of second medium w.r.t the first medium.  Absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v) i.e. n = c / v  Relative refractive index of medium. 2 w.r.t. the medium 1 is defined as the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). i.e. n21= v2 / v1

 Light is a form of energy which produces the sensation of sight.  Speed of light in vacuum / air = 3 × 108 ms–1  Ray of light : A line drawn in the direction of propagation of light is called ray of light.  Beam of light : A group of parallel rays light emitted by a source of light is called beam of light.  Reflection of light : The phenomenon of returning of light in the same medium after striking a surface is called reflection of light.  Laws of reflection : The reflection of light from a surface obeys certain laws called laws of reflection. (i) incident angle is equal to reflected angle i.e. i = r. (ii) Incident ray, reflected ray and normal to the reflecting surface at the point on incident lie in the same plane.  Concave mirror : concave mirror is a part of a hollow sphere whose outer part is silvered and the inner part is reflecting surface.  Convex mirror : convex mirror is a part of a hollow sphere whose outer part is reflecting surface and inner part is silvered.  Centre of curvature : The centre of a hollow sphere of which the spherical mirror forms a part is called centre of curvature. It is denoted by C  Radius of curvature : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature. It is denoted by R  Pole : The mid point of a spherical mirror is called its pole. It is denoted by P  Aperture: The part of spherical mirror exposed to the incident light is called the aperture of the mirror.  Principal Axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror and extend on either side is called principal axis of the spherical mirror.  Principal Focus : A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appears to meet after reflection from the spherical mirror is called principal focus. It is denoted by F.  Focal Plane : A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of the spherical mirror is called focal plane of the spherical mirror.  Focal length (f): The distance between the pole (P) and the principal focus (F) of a spherical mirror is called the focal length of the spherical mirror.  f = , Where R is the radius of the curvature of the mirror.  Focal length and radius of curvature of a concave mirror are negative.  Focal length and radius of curvature of a convex mirror are positive.  Sign Conventions for reflection by spherical mirrors (1) All distance are measured from the pole of a spherical mirror. (2) Distance measured in the direction of incident light are taken as positive. Distance measured in the direction opposite to that of the incident light are taken negative. (3) The upward distance perpendicular to the principal axis are taken as positive, while the downward distance perpendicular to the principal axis are taken as negative.  Radius of curvature plane mirror =  ( infinite)  Focal length of a plane mirror =   Mirror Formula : The relation between u, v, and focal length (f) of a spherical mirror is known as mirror formula. That is  Linear magnification : Linear magnification produced by a mirror is defined as the ratio of the size ( or height) of the image to the size of the object . It is denoted by m. That is  Power of mirror (P) = =  Linear magnification produced by a plane mirror = + 1.  Refraction of light: The bending of light rays when they pass obsessively from one medium to the other medium is called refraction of light .  A transparent medium through which light travels fast is known as optically rarer medium.  A transparent medium through which light travels slow is known as optically denser medium.  Laws of refraction (i) The incident ray, the refracted ray and the normal to the surface separating two media all lie in the same plane. (ii) The ratio of the sine of the incident angle (i) to the sine of the refracted angle (r) is constant i.e. sin i/ sin r = constant This constant is known as the refractive index of second medium w.r.t the first medium.  Absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v) i.e. n = c / v  Relative refractive index of medium. 2 w.r.t. the medium 1 is defined as the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). i.e. n21= v2 / v1

 Energy is the essential requirement for each and every activity in our life.  The various sources of energy are the sun, the wind, water, fossil fuels etc.  The sun is the ultimate source of all forms of energy.  A good source of energy is one which supplies large amount of useful energy, easily available, economical and cause minimum environmental pollution. .  Thermal power plant generates electricity by burning fossil fuel like coal and oil.  LPG is a petroleum gas liquefied under pressure. Its full form is liquefied Petroleum Gas.  CNG is compressed Natural Gas.  Main constituents of CNG is methane.  Electricity produced by flowing water is known as hydro - electric power.  A plant used to produce hydro -electric power is known as hydro -electric power plant.  Potential energy of water stored in a dam is converted into kinetic energy of the falling water. This kinetic energy of falling water is converted into the kinetic energy of the armature of the generator which in turn is converted into electric energy.  Biomass is material which contains carbon and other combustible material.  Plants, wood animals and plants waster are the examples of biomass.  Gobar gas or bio-gas is the example of a bio - mass energy source.  Main constituent of a biogas or gobar gas is a methane gas.  Biogas plant is of two types: (a) Fixed-dome type, (b) Floating gas holder type.  Kinetic energy of wind is known as wind energy.  Wind energy is used to produce electricity.  The region where large number of wind mills are erected to produce electricity is called wind energy farm.  The minimum speed of wind to operate generator to produce electricity is about 15 km/h.  Constant and rapid use of conventional sources of energy would ultimately exhaust these sources and hence a need for tapping energy from alternate or non-conventional sources of energy is seriously felt.  Solar energy is the energy emitted by the sun in the form of heat and light.  Solar constant is defined as the energy received from the sun in one second by a unit square metre area of the outer edge of earth's atmosphere exposed perpendicular to the radiation of the sun at an average distance between the sun and the earth.  Value of solar constant = 1.4 k W/m2.  Solar devices like solar cooker, solar furnace, solar water heater, solar panels and solar cells are used to harness solar energy.  Water due to its high specific heat capacity (4200 J kg–1°C–1) is a store house of heat energy.  Energy from sea or ocean water is available in the form of (i) energy of sea waves (ii) Tidal energy and (iii) Ocean thermal energy (OTE).  The heat energy obtained from the conversion of nuclear mass is known as nuclear energy.  Nuclear energy is obtained by two processes known as nuclear fission and nuclear fusion.  Nuclear energy is expressed in electron - volt(eV) 1 eV = 1.6  10–19J 1 MeV = 106 eV = 1.6 –13J  Nuclear Fission is the process of splitting a heavy nucleus (say Uranium) into two comparatively lower nuclei along with the release of large amount energy when bombarded with thermal neutron.  Nuclear reactor is a device used to carry out controlled chain reaction.  Nuclear fusion is the process of fusing or combining together two small nuclei to form a comparatively big nucleus with the release of large energy.  Nuclear fusion reactions occur at very high temperature (107K).  Nuclear fusion reactions occurring in the interior of the sun are responsible for the energy of the sun. In other words, nuclear fusion reactions are the sources of energy of the sun.  Sources of energy are classified into two categories (i) conventional or non-renewable sources of energy and (ii) Non-conventional or renewable sources of energy.  Extraction and transportation of energy from various sources of energy cause environmental pollution.  The energy from various sources of energy must be used effectively to conserve energy.

 Energy is the essential requirement for each and every activity in our life.  The various sources of energy are the sun, the wind, water, fossil fuels etc.  The sun is the ultimate source of all forms of energy.  A good source of energy is one which supplies large amount of useful energy, easily available, economical and cause minimum environmental pollution. .  Thermal power plant generates electricity by burning fossil fuel like coal and oil.  LPG is a petroleum gas liquefied under pressure. Its full form is liquefied Petroleum Gas.  CNG is compressed Natural Gas.  Main constituents of CNG is methane.  Electricity produced by flowing water is known as hydro - electric power.  A plant used to produce hydro -electric power is known as hydro -electric power plant.  Potential energy of water stored in a dam is converted into kinetic energy of the falling water. This kinetic energy of falling water is converted into the kinetic energy of the armature of the generator which in turn is converted into electric energy.  Biomass is material which contains carbon and other combustible material.  Plants, wood animals and plants waster are the examples of biomass.  Gobar gas or bio-gas is the example of a bio - mass energy source.  Main constituent of a biogas or gobar gas is a methane gas.  Biogas plant is of two types: (a) Fixed-dome type, (b) Floating gas holder type.  Kinetic energy of wind is known as wind energy.  Wind energy is used to produce electricity.  The region where large number of wind mills are erected to produce electricity is called wind energy farm.  The minimum speed of wind to operate generator to produce electricity is about 15 km/h.  Constant and rapid use of conventional sources of energy would ultimately exhaust these sources and hence a need for tapping energy from alternate or non-conventional sources of energy is seriously felt.  Solar energy is the energy emitted by the sun in the form of heat and light.  Solar constant is defined as the energy received from the sun in one second by a unit square metre area of the outer edge of earth's atmosphere exposed perpendicular to the radiation of the sun at an average distance between the sun and the earth.  Value of solar constant = 1.4 k W/m2.  Solar devices like solar cooker, solar furnace, solar water heater, solar panels and solar cells are used to harness solar energy.  Water due to its high specific heat capacity (4200 J kg–1°C–1) is a store house of heat energy.  Energy from sea or ocean water is available in the form of (i) energy of sea waves (ii) Tidal energy and (iii) Ocean thermal energy (OTE).  The heat energy obtained from the conversion of nuclear mass is known as nuclear energy.  Nuclear energy is obtained by two processes known as nuclear fission and nuclear fusion.  Nuclear energy is expressed in electron - volt(eV) 1 eV = 1.6  10–19J 1 MeV = 106 eV = 1.6 –13J  Nuclear Fission is the process of splitting a heavy nucleus (say Uranium) into two comparatively lower nuclei along with the release of large amount energy when bombarded with thermal neutron.  Nuclear reactor is a device used to carry out controlled chain reaction.  Nuclear fusion is the process of fusing or combining together two small nuclei to form a comparatively big nucleus with the release of large energy.  Nuclear fusion reactions occur at very high temperature (107K).  Nuclear fusion reactions occurring in the interior of the sun are responsible for the energy of the sun. In other words, nuclear fusion reactions are the sources of energy of the sun.  Sources of energy are classified into two categories (i) conventional or non-renewable sources of energy and (ii) Non-conventional or renewable sources of energy.  Extraction and transportation of energy from various sources of energy cause environmental pollution.  The energy from various sources of energy must be used effectively to conserve energy.

 Hans Christian oersted discovered a relationship between electricity and magnetism.  A current carrying wire behaves as a magnet.  When a current passes through a wire, a magnetic field is set up around the wire. This effect of current is called magnetic effect of current.  Like magnetic poles repel each other and unlike magnetic poles attract each other.  Magnetic field is space or region around a current carrying wire or a magnet within which its influence is felt by another magnet.  Magnetic field line : The path along which a free unit north pole moves in a magnetic field is called magnetic field line. The tangent at any point on a magnetic field line gives the direction of the magnetic field at that point.  Two magnetic field lines can't intersect or cross each other.  Magnetic field lines are crowded in a region of strong magnetic field.  Magnetic field lines are far apart in a region of weak magnetic field.  When current passes through a straight wire or conductor, a magnetic field is set up around the wire or conductor.  Magnetic field around a current carrying wire or conductor is represented by concentric circles centred at the wire or the conductor.  The direction of magnetic field around the current carrying conductor is determined by Right Hand Thumb Rule.  Magnetic field around a current carrying wire increases with the increase in the current passing through the wire.  Magnetic field around a current carrying wire or conductor is represented by concentric circles centred at the wire or the conductor.  The direction of magnetic field around the current carrying conductor is determined by Right Hand Thumb Rule.  Magnetic field around a current carrying wire increases with the increase in the current passing through the wire.  Magnetic field around a current carrying wire decreases as we go away from the wire.  Magnetic field due to a very long wire like a power transmission line carrying current I and at a distance r from the wire is given by B = ; where, µ0 = 4 × 10–7 TmA–1  Two parallel wires or conductors carrying current in the same directs attract each other.  Two parallel wires or conductors carrying current in the opposite directions repel each other.  The magnetic field around a straight current carrying conductor or wire can be increased by bending it into a circular loop.  The strength of magnetic field produced at the centre of a circular loop of a wire is (i) directly proportional to the amount of current passing through the loop of the wire. (ii) directly proportional to the number of turns of the circular loop of the wire. (iii) inversely proportional to the radius of the circular loop of the wire.  Magnetic field produced by a current carrying circular wire or loop decreases on both sides along the axis of the circular wire.  A solenoid is a coil of many turns of an insulated copper wire closely wound in the shape of a tight spring.  Magnetic field inside a current carrying solenoid is uniform magnetic field.  A solenoid carrying current behaves like a bar magnet.  A soft iron rod placed in a current carrying solenoid is known as electromagnet.  A current carrying conductor placed perpendicular to the magnetic field experience a force.  The force acting on a current carrying conductor placed perpendicular to the magnetic field B is given by F = BIl  Direction of force experienced by a current carrying conductor placed in a magnetic field is determined by Fleming’s Left Hand Rule.  No Force acts on a current carrying conductor when placed parallel to the magnetic field.  SI unit of magnetic field is tesla (T).  Force acts on a charge moving perpendicular to the magnetic field. This force is called Lorentz force.  Force acting on a charge Q moving with velocity v perpendicular to the magnetic field B is given by F = BQV  No force acts on a charge moving parallel to the magnetic field B.  Direction of force experienced by a moving charge in a magnetic field is determined by Right Hand Rule.  Electric motor is a device which converts electrical energy into mechanical energy.  Principle of electric motor : Electric motor works on the principle that a current carrying conductor placed perpendicular to a magnetic field experiences a force.  The phenomenon of producing induced current in a closed circuit due to the change in magnetic field in the circuit is known as electromagnetic induction.  More induced current flows through a closed coil if a bar magnet is brought towards or away from the coil with large speed.  No induced current flows through a closed coil if magnetic field linked with it does not change.  Direction of induced current in a conductor is determined by Fleming’s Right hand rule.  Direct current is an electric current whose magnitude is either constant or variable but the direction of flow in a conductor remains the same.  Frequency of direct current is zero.  Alternating current is an electric current whose magnitude changes with time and direction reverse periodically.  In India, frequency of A.C. is 50 Hz.  A.C. is more dangerous than D.C.  Electric generator is a device used to convert mechanical energy into electrical energy.  Electric generator works on the principle of electromagnetic induction.  To supply electric power from one place to another place, three wires known as phase wire (or live wire), neutral wire and earth wire are used.  The potential difference between the live wire and neutral wire in a household supply of electric power is 220 V.  Current rating of a fuse is the maximum amount of electric current that can be passed through the fuse wire without melting it.  Current rating of a fuse wire in a circuit having bulbs and tubes is 5A.  Current rating of a fuse wire in a circuit having heating appliances is 15A.  Electric fuse is a safety device used to save the electrical appliances from burning when large current flows in the circuit.  Electric fuse is made of a material of low melting point.  Material used for making a fuse wire is made of copper / aluminium / tin-lead alloy.  Short Circuiting : When live wire and neutral wire come in direct contact, the resistance of the circuit becomes very small. Hence huge current flows through the circuit. This huge current produces large amount of heat in the circuit and the circuit catches fire. This is known as short circuiting.

 Hans Christian oersted discovered a relationship between electricity and magnetism.  A current carrying wire behaves as a magnet.  When a current passes through a wire, a magnetic field is set up around the wire. This effect of current is called magnetic effect of current.  Like magnetic poles repel each other and unlike magnetic poles attract each other.  Magnetic field is space or region around a current carrying wire or a magnet within which its influence is felt by another magnet.  Magnetic field line : The path along which a free unit north pole moves in a magnetic field is called magnetic field line. The tangent at any point on a magnetic field line gives the direction of the magnetic field at that point.  Two magnetic field lines can't intersect or cross each other.  Magnetic field lines are crowded in a region of strong magnetic field.  Magnetic field lines are far apart in a region of weak magnetic field.  When current passes through a straight wire or conductor, a magnetic field is set up around the wire or conductor.  Magnetic field around a current carrying wire or conductor is represented by concentric circles centred at the wire or the conductor.  The direction of magnetic field around the current carrying conductor is determined by Right Hand Thumb Rule.  Magnetic field around a current carrying wire increases with the increase in the current passing through the wire.  Magnetic field around a current carrying wire or conductor is represented by concentric circles centred at the wire or the conductor.  The direction of magnetic field around the current carrying conductor is determined by Right Hand Thumb Rule.  Magnetic field around a current carrying wire increases with the increase in the current passing through the wire.  Magnetic field around a current carrying wire decreases as we go away from the wire.  Magnetic field due to a very long wire like a power transmission line carrying current I and at a distance r from the wire is given by B = ; where, µ0 = 4 × 10–7 TmA–1  Two parallel wires or conductors carrying current in the same directs attract each other.  Two parallel wires or conductors carrying current in the opposite directions repel each other.  The magnetic field around a straight current carrying conductor or wire can be increased by bending it into a circular loop.  The strength of magnetic field produced at the centre of a circular loop of a wire is (i) directly proportional to the amount of current passing through the loop of the wire. (ii) directly proportional to the number of turns of the circular loop of the wire. (iii) inversely proportional to the radius of the circular loop of the wire.  Magnetic field produced by a current carrying circular wire or loop decreases on both sides along the axis of the circular wire.  A solenoid is a coil of many turns of an insulated copper wire closely wound in the shape of a tight spring.  Magnetic field inside a current carrying solenoid is uniform magnetic field.  A solenoid carrying current behaves like a bar magnet.  A soft iron rod placed in a current carrying solenoid is known as electromagnet.  A current carrying conductor placed perpendicular to the magnetic field experience a force.  The force acting on a current carrying conductor placed perpendicular to the magnetic field B is given by F = BIl  Direction of force experienced by a current carrying conductor placed in a magnetic field is determined by Fleming’s Left Hand Rule.  No Force acts on a current carrying conductor when placed parallel to the magnetic field.  SI unit of magnetic field is tesla (T).  Force acts on a charge moving perpendicular to the magnetic field. This force is called Lorentz force.  Force acting on a charge Q moving with velocity v perpendicular to the magnetic field B is given by F = BQV  No force acts on a charge moving parallel to the magnetic field B.  Direction of force experienced by a moving charge in a magnetic field is determined by Right Hand Rule.  Electric motor is a device which converts electrical energy into mechanical energy.  Principle of electric motor : Electric motor works on the principle that a current carrying conductor placed perpendicular to a magnetic field experiences a force.  The phenomenon of producing induced current in a closed circuit due to the change in magnetic field in the circuit is known as electromagnetic induction.  More induced current flows through a closed coil if a bar magnet is brought towards or away from the coil with large speed.  No induced current flows through a closed coil if magnetic field linked with it does not change.  Direction of induced current in a conductor is determined by Fleming’s Right hand rule.  Direct current is an electric current whose magnitude is either constant or variable but the direction of flow in a conductor remains the same.  Frequency of direct current is zero.  Alternating current is an electric current whose magnitude changes with time and direction reverse periodically.  In India, frequency of A.C. is 50 Hz.  A.C. is more dangerous than D.C.  Electric generator is a device used to convert mechanical energy into electrical energy.  Electric generator works on the principle of electromagnetic induction.  To supply electric power from one place to another place, three wires known as phase wire (or live wire), neutral wire and earth wire are used.  The potential difference between the live wire and neutral wire in a household supply of electric power is 220 V.  Current rating of a fuse is the maximum amount of electric current that can be passed through the fuse wire without melting it.  Current rating of a fuse wire in a circuit having bulbs and tubes is 5A.  Current rating of a fuse wire in a circuit having heating appliances is 15A.  Electric fuse is a safety device used to save the electrical appliances from burning when large current flows in the circuit.  Electric fuse is made of a material of low melting point.  Material used for making a fuse wire is made of copper / aluminium / tin-lead alloy.  Short Circuiting : When live wire and neutral wire come in direct contact, the resistance of the circuit becomes very small. Hence huge current flows through the circuit. This huge current produces large amount of heat in the circuit and the circuit catches fire. This is known as short circuiting.

 Light is a form of energy which produces the sensation of sight.  Speed of light in vacuum / air = 3 × 108 ms–1  Ray of light : A line drawn in the direction of propagation of light is called ray of light.  Beam of light : A group of parallel rays light emitted by a source of light is called beam of light.  Reflection of light : The phenomenon of returning of light in the same medium after striking a surface is called reflection of light.  Laws of reflection : The reflection of light from a surface obeys certain laws called laws of reflection. (i) incident angle is equal to reflected angle i.e. i = r. (ii) Incident ray, reflected ray and normal to the reflecting surface at the point on incident lie in the same plane.  Concave mirror : concave mirror is a part of a hollow sphere whose outer part is silvered and the inner part is reflecting surface.  Convex mirror : convex mirror is a part of a hollow sphere whose outer part is reflecting surface and inner part is silvered.  Centre of curvature : The centre of a hollow sphere of which the spherical mirror forms a part is called centre of curvature. It is denoted by C  Radius of curvature : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature. It is denoted by R  Pole : The mid point of a spherical mirror is called its pole. It is denoted by P  Aperture: The part of spherical mirror exposed to the incident light is called the aperture of the mirror.  Principal Axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror and extend on either side is called principal axis of the spherical mirror.  Principal Focus : A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appears to meet after reflection from the spherical mirror is called principal focus. It is denoted by F.  Focal Plane : A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of the spherical mirror is called focal plane of the spherical mirror.  Focal length (f): The distance between the pole (P) and the principal focus (F) of a spherical mirror is called the focal length of the spherical mirror.  f = , Where R is the radius of the curvature of the mirror.  Focal length and radius of curvature of a concave mirror are negative.  Focal length and radius of curvature of a convex mirror are positive.  Sign Conventions for reflection by spherical mirrors (1) All distance are measured from the pole of a spherical mirror. (2) Distance measured in the direction of incident light are taken as positive. Distance measured in the direction opposite to that of the incident light are taken negative. (3) The upward distance perpendicular to the principal axis are taken as positive, while the downward distance perpendicular to the principal axis are taken as negative.  Radius of curvature plane mirror =  ( infinite)  Focal length of a plane mirror =   Mirror Formula : The relation between u, v, and focal length (f) of a spherical mirror is known as mirror formula. That is  Linear magnification : Linear magnification produced by a mirror is defined as the ratio of the size ( or height) of the image to the size of the object . It is denoted by m. That is  Power of mirror (P) = =  Linear magnification produced by a plane mirror = + 1.  Refraction of light: The bending of light rays when they pass obsessively from one medium to the other medium is called refraction of light .  A transparent medium through which light travels fast is known as optically rarer medium.  A transparent medium through which light travels slow is known as optically denser medium.  Laws of refraction (i) The incident ray, the refracted ray and the normal to the surface separating two media all lie in the same plane. (ii) The ratio of the sine of the incident angle (i) to the sine of the refracted angle (r) is constant i.e. sin i/ sin r = constant This constant is known as the refractive index of second medium w.r.t the first medium.  Absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v) i.e. n = c / v  Relative refractive index of medium. 2 w.r.t. the medium 1 is defined as the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). i.e. n21= v2 / v1

 Light is a form of energy which produces the sensation of sight.  Speed of light in vacuum / air = 3 × 108 ms–1  Ray of light : A line drawn in the direction of propagation of light is called ray of light.  Beam of light : A group of parallel rays light emitted by a source of light is called beam of light.  Reflection of light : The phenomenon of returning of light in the same medium after striking a surface is called reflection of light.  Laws of reflection : The reflection of light from a surface obeys certain laws called laws of reflection. (i) incident angle is equal to reflected angle i.e. i = r. (ii) Incident ray, reflected ray and normal to the reflecting surface at the point on incident lie in the same plane.  Concave mirror : concave mirror is a part of a hollow sphere whose outer part is silvered and the inner part is reflecting surface.  Convex mirror : convex mirror is a part of a hollow sphere whose outer part is reflecting surface and inner part is silvered.  Centre of curvature : The centre of a hollow sphere of which the spherical mirror forms a part is called centre of curvature. It is denoted by C  Radius of curvature : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature. It is denoted by R  Pole : The mid point of a spherical mirror is called its pole. It is denoted by P  Aperture: The part of spherical mirror exposed to the incident light is called the aperture of the mirror.  Principal Axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror and extend on either side is called principal axis of the spherical mirror.  Principal Focus : A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appears to meet after reflection from the spherical mirror is called principal focus. It is denoted by F.  Focal Plane : A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of the spherical mirror is called focal plane of the spherical mirror.  Focal length (f): The distance between the pole (P) and the principal focus (F) of a spherical mirror is called the focal length of the spherical mirror.  f = , Where R is the radius of the curvature of the mirror.  Focal length and radius of curvature of a concave mirror are negative.  Focal length and radius of curvature of a convex mirror are positive.  Sign Conventions for reflection by spherical mirrors (1) All distance are measured from the pole of a spherical mirror. (2) Distance measured in the direction of incident light are taken as positive. Distance measured in the direction opposite to that of the incident light are taken negative. (3) The upward distance perpendicular to the principal axis are taken as positive, while the downward distance perpendicular to the principal axis are taken as negative.  Radius of curvature plane mirror =  ( infinite)  Focal length of a plane mirror =   Mirror Formula : The relation between u, v, and focal length (f) of a spherical mirror is known as mirror formula. That is  Linear magnification : Linear magnification produced by a mirror is defined as the ratio of the size ( or height) of the image to the size of the object . It is denoted by m. That is  Power of mirror (P) = =  Linear magnification produced by a plane mirror = + 1.  Refraction of light: The bending of light rays when they pass obsessively from one medium to the other medium is called refraction of light .  A transparent medium through which light travels fast is known as optically rarer medium.  A transparent medium through which light travels slow is known as optically denser medium.  Laws of refraction (i) The incident ray, the refracted ray and the normal to the surface separating two media all lie in the same plane. (ii) The ratio of the sine of the incident angle (i) to the sine of the refracted angle (r) is constant i.e. sin i/ sin r = constant This constant is known as the refractive index of second medium w.r.t the first medium.  Absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v) i.e. n = c / v  Relative refractive index of medium. 2 w.r.t. the medium 1 is defined as the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). i.e. n21= v2 / v1

 Light is a form of energy which produces the sensation of sight.  Speed of light in vacuum / air = 3 × 108 ms–1  Ray of light : A line drawn in the direction of propagation of light is called ray of light.  Beam of light : A group of parallel rays light emitted by a source of light is called beam of light.  Reflection of light : The phenomenon of returning of light in the same medium after striking a surface is called reflection of light.  Laws of reflection : The reflection of light from a surface obeys certain laws called laws of reflection. (i) incident angle is equal to reflected angle i.e. i = r. (ii) Incident ray, reflected ray and normal to the reflecting surface at the point on incident lie in the same plane.  Concave mirror : concave mirror is a part of a hollow sphere whose outer part is silvered and the inner part is reflecting surface.  Convex mirror : convex mirror is a part of a hollow sphere whose outer part is reflecting surface and inner part is silvered.  Centre of curvature : The centre of a hollow sphere of which the spherical mirror forms a part is called centre of curvature. It is denoted by C  Radius of curvature : The radius of a hollow sphere of which the spherical mirror forms a part is called radius of curvature. It is denoted by R  Pole : The mid point of a spherical mirror is called its pole. It is denoted by P  Aperture: The part of spherical mirror exposed to the incident light is called the aperture of the mirror.  Principal Axis: A line joining the centre of curvature (C) and pole (P) of a spherical mirror and extend on either side is called principal axis of the spherical mirror.  Principal Focus : A point on the principal axis of a spherical mirror where the rays of light parallel to the principal axis meet or appears to meet after reflection from the spherical mirror is called principal focus. It is denoted by F.  Focal Plane : A plane normal or perpendicular to the principal axis and passing through the principal focus (F) of the spherical mirror is called focal plane of the spherical mirror.  Focal length (f): The distance between the pole (P) and the principal focus (F) of a spherical mirror is called the focal length of the spherical mirror.  f = , Where R is the radius of the curvature of the mirror.  Focal length and radius of curvature of a concave mirror are negative.  Focal length and radius of curvature of a convex mirror are positive.  Sign Conventions for reflection by spherical mirrors (1) All distance are measured from the pole of a spherical mirror. (2) Distance measured in the direction of incident light are taken as positive. Distance measured in the direction opposite to that of the incident light are taken negative. (3) The upward distance perpendicular to the principal axis are taken as positive, while the downward distance perpendicular to the principal axis are taken as negative.  Radius of curvature plane mirror =  ( infinite)  Focal length of a plane mirror =   Mirror Formula : The relation between u, v, and focal length (f) of a spherical mirror is known as mirror formula. That is  Linear magnification : Linear magnification produced by a mirror is defined as the ratio of the size ( or height) of the image to the size of the object . It is denoted by m. That is  Power of mirror (P) = =  Linear magnification produced by a plane mirror = + 1.  Refraction of light: The bending of light rays when they pass obsessively from one medium to the other medium is called refraction of light .  A transparent medium through which light travels fast is known as optically rarer medium.  A transparent medium through which light travels slow is known as optically denser medium.  Laws of refraction (i) The incident ray, the refracted ray and the normal to the surface separating two media all lie in the same plane. (ii) The ratio of the sine of the incident angle (i) to the sine of the refracted angle (r) is constant i.e. sin i/ sin r = constant This constant is known as the refractive index of second medium w.r.t the first medium.  Absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v) i.e. n = c / v  Relative refractive index of medium. 2 w.r.t. the medium 1 is defined as the ratio of the speed of light in medium 1 (v1) to the speed of light in medium 2 (v2). i.e. n21= v2 / v1

Source of Energy  Energy is the essential requirement for each and every activity in our life.  The various sources of energy are the sun, the wind, water, fossil fuels etc.  The sun is the ultimate source of all forms of energy.  A good source of energy is one which supplies large amount of useful energy, easily available, economical and cause minimum environmental pollution. .  Thermal power plant generates electricity by burning fossil fuel like coal and oil.  LPG is a petroleum gas liquefied under pressure. Its full form is liquefied Petroleum Gas.  CNG is compressed Natural Gas.  Main constituents of CNG is methane.  Electricity produced by flowing water is known as hydro - electric power.  A plant used to produce hydro -electric power is known as hydro -electric power plant.  Potential energy of water stored in a dam is converted into kinetic energy of the falling water. This kinetic energy of falling water is converted into the kinetic energy of the armature of the generator which in turn is converted into electric energy.  Biomass is material which contains carbon and other combustible material.  Plants, wood animals and plants waster are the examples of biomass.  Gobar gas or bio-gas is the example of a bio - mass energy source.  Main constituent of a biogas or gobar gas is a methane gas.  Biogas plant is of two types: (a) Fixed-dome type, (b) Floating gas holder type.  Kinetic energy of wind is known as wind energy.  Wind energy is used to produce electricity.  The region where large number of wind mills are erected to produce electricity is called wind energy farm.  The minimum speed of wind to operate generator to produce electricity is about 15 km/h.  Constant and rapid use of conventional sources of energy would ultimately exhaust these sources and hence a need for tapping energy from alternate or non-conventional sources of energy is seriously felt.  Solar energy is the energy emitted by the sun in the form of heat and light.  Solar constant is defined as the energy received from the sun in one second by a unit square metre area of the outer edge of earth's atmosphere exposed perpendicular to the radiation of the sun at an average distance between the sun and the earth.  Value of solar constant = 1.4 k W/m2.  Solar devices like solar cooker, solar furnace, solar water heater, solar panels and solar cells are used to harness solar energy.  Water due to its high specific heat capacity (4200 J kg–1°C–1) is a store house of heat energy.  Energy from sea or ocean water is available in the form of (i) energy of sea waves (ii) Tidal energy and (iii) Ocean thermal energy (OTE).  The heat energy obtained from the conversion of nuclear mass is known as nuclear energy.  Nuclear energy is obtained by two processes known as nuclear fission and nuclear fusion.  Nuclear energy is expressed in electron - volt(eV) 1 eV = 1.6  10–19J 1 MeV = 106 eV = 1.6 –13J  Nuclear Fission is the process of splitting a heavy nucleus (say Uranium) into two comparatively lower nuclei along with the release of large amount energy when bombarded with thermal neutron.  Nuclear reactor is a device used to carry out controlled chain reaction.  Nuclear fusion is the process of fusing or combining together two small nuclei to form a comparatively big nucleus with the release of large energy.  Nuclear fusion reactions occur at very high temperature (107K).  Nuclear fusion reactions occurring in the interior of the sun are responsible for the energy of the sun. In other words, nuclear fusion reactions are the sources of energy of the sun.  Sources of energy are classified into two categories (i) conventional or non-renewable sources of energy and (ii) Non-conventional or renewable sources of energy.  Extraction and transportation of energy from various sources of energy cause environmental pollution.  The energy from various sources of energy must be used effectively to conserve energy.