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Physics
Physics Class 10 CISCE
| Term | Definition |
|---|---|
| Why do molecules possess kinetic energy? | Due to their random motion |
| Why do molecules possess potential energy? | Due to their molecular attractive forces. |
| Internal Energy | Sum of potential and kinetic of a molecule |
| Thermal energy | Total internal energy of all the molecules of a substance |
| What happens to the internal energies of a hot body and a cold body when they are kept in contact | hot body-decreases cold body-increases |
| Heat | The form of energy that flows from a hot body to a cold body when they are kept in contact |
| Calorimetry | The measurement of quantity of heat |
| SI Unit of Heat | Joule |
| Most commonly used unit of heat | Calorie |
| Why is calorie defined in terms of a specific temperature | Due to non uniform expansion of water |
| Calorie | Heat energy required to raise the temperature of 1g of water from 14.5 to 15.5 degree celsius |
| Relation between calorie and joule | 1 cal=4.2J 1J=0.24cal |
| ___________ is used to measure the energy value of foods. | kilo calorie |
| Temperature | Parameter which tells the thermal state of a body and determines the direction of flow of heat when two bodies at different temperatures are kept in contact |
| Thermal Equilibrium | When the two bodies in contact are of the same temperature and there is no flow of heat |
| SI Unit of Temperature | kelvin |
| Formula for conversion between different units | c/5=f-32/9=k-273/5 |
| Why is temperature difference in C and K the same? | Since the temperature on the two scales differ by a constant number. |
| Factors affecting quantity of heat absorbed | 1. mass of the body 2. rise in temperature of the body 3. material or substance of the body |
| ____________ is measured by the principle of calorimetry and __________ is measured using a thermometer | heat temperature |
| When two bodies are placed in contact total amount of heat is ____________ | sum of heat of individual body |
| When two bodies at different temperatures are kept in contact the resultant temperature is ____________ | temperature between two temperatures |
| Temperature of a body depends on __________ | average kinetic energy of the molecules |
| Heat capacity | Heat capacity of a substance is the amount of heat required to raise the temperature of the body through 1 degree celcius |
| SI unit of heat capacity | J/K J/C |
| __________ is a characteristic property of a substance that affects the heat absorbed by it. | specific heat capacity |
| Q=______________ | mc[delta]T |
| C'=________ | Q/[delta]T=mc |
| c=___________ | Q/m*[delta]T |
| Specific Heat capacity | The amount of heat energy required to raise the temperature of unit mass of a substance by 1 degree celcius |
| SI Unit of specific heat capacity | J/KgK J/kg/C |
| Heat capacity depends on _____________ | mass and specific heat capacity |
| Good conductor of heat has a _______ specific heat capacity and a poor conductor has a _________ specific heat capacity | low high |
| Why is a conductor of low specific heat capacity better than one with high specific heat capacity? | Because it shows a rapid and high rise in temperature while the one with high c shows a slow and small rise in temperature when the equal amount of heat energy is absorbed |
| _________ has an unusually high specific heat capacity of ________ | water 4200J/Kg/K |
| Calorimeter | A cylindrical vessel which is used to measure the heat gained or lost by a substance when it is mixed with another substance or body |
| Calorimeter is made of a thin sheet of __________ | Copper |
| Why is copper used in a calormieter? | 1. Copper is a good conductor therefor it quickly acquires the temperatures of its contents 2. Copper has a low specific heat capacity therefore the enrgy required by the calorimeter to acquire the temperature of its contents is less |
| How is heat loss by radiation prevented in a calorimeter? | Outer and inner surfaces of the vessels are polished |
| How is heat loss by convection prevented in a calorimeter? | The vessel is covered with a wooden lid |
| How is heat loss by conduction prevented in a calorimeter? | The space between the wooden jacket and the vessel is filled with some poor conductor like wool |
| How is a calorimeter insulated? | Vessel is placed in a wooden jacket |
| Principle of calorimetry is also called ________ | Principle of method of mixtures |
| Principle of calorimetry | Heat lost by the hot body= Heat gained by the cold body |
| Mathematical statement for principle of method of mixtures | m1c1(t1-t)=m2c2(t-t2) |
| Why is climate near the sea moderate? | Specific heat capacity of water is 5 times that of sand. Therefor sand gets heated or cooled more rapidly thus creating large difference in temperature causing air currents by convection. This brings about breeze which are responsible for moderate climate |
| Hot water bags are used for fomentation. Why? | Due to high specific heat capacity of water, it does not cool quickly. Thus it provides more heat over a longer period. |
| Water is used as an effective coolant. Why? | Water can be used in pipes around the heated parts of a machine to cool it and water absorbs more heat from surroundings without much rise in temperature due to the high specific capacity of heat |
| Radiators in car and generators use water for cooling. Why? | Water can be used in pipes around the heated parts of a machine to cool it and water absorbs more heat from surroundings without much rise in temperature due to the high specific capacity of heat |
| Why is water used as a reservoir to prevent wine from freezing? | Water has to impart a large amount of energy before reaching its freezing point therefore it keeps the bottles warm |
| Farmers fill their fields with water during winter. Why? | In winter when temperature falls to 0celcius or below, the water in capillaries of plants freeze and expand - the veins bursts and the plant dies. Due to high specific heat capacity of water it does not allow the temperature in the plants to fall to 0 |
| Why do plants and animals have a lot of water content in them? | It helps to maintain same body temperature in all seasons. |
| Why are the bases of cooking pans made thick? | So that the specific heat capacity becomes larger which allows slow and small rise in temperature which is essential for proper cooking. It also keeps the food warm longer |
| Base of an electric press is made thick and heavy | So that it remains hot longer even after the current supply is stopped |
| Change of phase | The process of change from one state to another state at a constant temperature. |
| Change of phase is brought about by _________ | exchange of heat |
| Melting/Fusion | The change of state of a substance from solid state to liquid state by the absorption of heat at a constant temperature |
| Melting point | The constant temperature at which a solid changes to liquid state on absorption of heat |
| Freezing | The change of state of a substance from liquid state to solid state by the liberation of heat at a constant temperature |
| Freezing point | The constant temperature at which a liquid changes to solid state on liberation of heat ᓚᘏᗢ |
| For a _________ substance melting and freezing points are the same | pure |
| Vaporisation/Boiling | The change of state of a substance from liquid state to gaseous state by the absorption of heat at a constant temperature |
| Condensation/Liquefaction | The change of state of a substance from gaseous state to liquid state by the liberation of heat at a constant temperature |
| Boiling Point | The constant temperature at which a liquid changes to gaseous state on absorption of heat |
| Condensation point | The constant temperature at which a gas changes to liquid state on liberation of heat |
| For a pure substance boiling point and _________ are same | Condensation point |
| Lead and wax _______ on melting while ice and bismuth _________ on melting | expand contract |
| Effect of pressure on the melting point of substances that expand on melting | Increases with increase in pressure |
| Effect of pressure on the melting point of substances that contract on melting | Decreases with increase in pressure |
| Effect of impurities on melting point | Decreases with presence of impurities |
| Why is salt added to ice while making kulfis? | Melting point of ice decreases with presence of impurities |
| All liquids ______ on boiling | expand |
| Boiling point is ________ proportional to pressure | directly |
| Why are vegetables cooked inside pressure cooker? | The vapors are not allowed to escape from the pressure cooker which increases the pressure inside, thus increasing boiling point of the water to 120- 125 C which makes cooking of vegetables faster and keeps them warm for a longer period |
| Why is cooking difficult at higher altitude? | Atmospheric pressure is very low therefore boiling point of water decreases thus food is cooked slowly and does not remain warm for too long |
| Effect of impurities on boiling point | Boiling point increases with presence of impurities |
| Why is salt added to the water while cooking pulses? | To increase boiling point and cook faster and keep warmer for longer period |
| Latent Heat | The heat absorbed or liberated during the change of phase which is not manifested externally by rise in temperature. |
| L=__________ | Q/m |
| Specific Latent Heat | The amount of heat energy absorbed or liberated by the unit mass of a substance during the change of phase at a constant temperature |
| SI unit of Specific Latent Heat | J/Kg |
| Specific Latent Heat of Fusion | Amount of energy required to melt unit mass of ice at 0C to water at 0C without any change in temperature |
| Specific Latent Heat of Freezing | Amount of energy released to freeze unit mass of water at 0C to ice at 0C without any change in temperature |
| For a ___________ specific latent heat of fusion and freezing are the same | pure |
| Why does temperature not rise during phase change? | All the heat energy is utilised in increasing the potential energy of the molecules |
| Why does the snow on mountains not melt all at once | Due to high specific latent heat of fusion of ice so it changes to water slowly |
| In cold countries lakes do not freeze at once. Why? | Due to high specific heat of fusion of ice the lake has to release a large amount of energy to the surrounding before freezing and the top layer of ice formed prevents further loss of energy |
| Drinks are cooled more by ice than water at 0C why? | Because ice absorbs large amount of energy to change into water at 0C due to its high specific latent heat of fusion |
| When a frozen lake starts melting, surrounding area becomes colder. Why? | Due to high specific latent heat of fusion of ice the lake absorbs large amounts of heat energy from the surroundings to melt. |
| It is colder after hail storm than during it. Why? | Due to high specific latent heat of fusion the ice starts absorbing large amounts of heat energy from the surroundings as it starts to melt |
| Why are electron orbits called stationary orbits? |
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