Thermal Capacity( Heat Capacity), Specific Heat Capacity, Latent Heat

------Thermal capacity( Heat capacity), specific heat capacity, latent heat, specific latent heat ------Thermal capacity(Heat capacity) of an object: Q: It is the amount of heat needed to raise the temperature of a substance by 10C. Units:J/0C

Thermal energy lost by the water=Q=mc

=250 x 4.2 x 20=21 000J 𝚫𝚫𝜽𝜽

Heat is conserved 21 000J

------Note: • If an object Y has a greater thermal capacity than object X, then this means that it also needs more heat energy to heat up and it will also lose more heat energy as it cools down to room temperature as compared to block X. • If equal masses of different liquids are heated to a same temperature rise but if liquid 2 takes twice as long as liquid 1, then the thermal capacity of liquid 1 is less than the thermal capacity of liquid 2. • In general if a thing gets heated up fast then it has low thermal capacity. ------

www.smarteduhub.com 1 Specific heat capacity of an object: C: It is the amount of heat needed to raise the temperature of one kg of a substance by 10C. Hence : = ( ) ( ) E= 𝑬𝑬 Units: J/kg0C 𝒎𝒎 𝜽𝜽𝟐𝟐−𝜽𝜽𝟏𝟏 𝟐𝟐 𝟏𝟏 Experiment:𝒄𝒄 ⟹ 𝒎𝒎𝒎𝒎 𝜽𝜽 − 𝜽𝜽 Suppose you need to find our specific heat capacity of aluminium. Take the following measurements: • mass of aluminium, • initial temperature ( ) • final temperature( ) of the 𝜽𝜽𝟏𝟏 aluminium block 𝜽𝜽𝟐𝟐 • Time (t) for which heat is supplied • Voltage(V) • Current(I) • Note that the formula for specific heat capacity is: = but since we do not have ( ) ; 𝑬𝑬 a joule meter we are calculating the value of E using the formula E=VIt 𝒎𝒎 𝜽𝜽𝟐𝟐−𝜽𝜽𝟏𝟏 𝒄𝒄 = = ( ) ( ) 𝑬𝑬 𝑽𝑽𝑽𝑽𝑽𝑽 If heat losses occur: 𝒄𝒄 𝒎𝒎 𝜽𝜽𝟐𝟐 − 𝜽𝜽𝟏𝟏 𝒎𝒎 𝜽𝜽𝟐𝟐 − 𝜽𝜽𝟏𝟏 If a lid is not present as shown in the above diagram then the value to specific heat capacity will be higher as more heat will be lost to the surroundings and hence the temperature rise will be less. So more heat will be needed to cause the same temperature rise.

Preventing heat losses: • Care should be taken to prevent heat losses to the environment by using lagging or insulation around the block. • By polishing the surface of the block or wrapping the block in a shiny material or it can be painted white • Reduce draughts ------

www.smarteduhub.com 2 ------If the following procedure is used to find the specific heat capacity of a given metal, then it will result in inaccuracy. This is because heat will be lost to the surroundings or the cup

------Note: Water has a very high specific heat capacity. This is a disadvantage for cooking because: • It will take long time to heat up • long time to cool down • expensive as it takes lot of energy to heat up,

------Latent heat of an object: The energy supplied to a substance when it undergoes a state change is said to be latent heat or hidden heat. Heat is said to be latent as there is no temperature rise during state change although heat is being supplied. ------

www.smarteduhub.com 3 ------Specific latent heat of fusion : It is the energy needed to melt 1kg of a substance at its melting point. E = ml Unit:J/kg In general; fusion means melting ------Experiment: to calculate the specific latent heat of fusion of ice: In this experiment, a low voltage heater is used to melt the crushed ice in a funnel. To take into account the heat transferred from the surroundings, the mass of the ice melted in a certain time must be measured with the heater on and then with the heater off. The difference in the two masses gives the mass of the ice melted due to the heater only. Suppose the mass

of melted ice with heater off=m1 and mass of melted ice with heater on =m2.Then m2- m1=m = mass of ice melted by the heater only.

[ Note that the time to record the masses m1 and m2 must be the same]

The formula for the specific latent heat of fusion:l= 𝑬𝑬 ------𝒎𝒎𝟐𝟐−𝒎𝒎𝟏𝟏 Numerical: ------

------

www.smarteduhub.com 4

------Specific latent heat of vaporisation: It is the energy needed to change 1kg of a substance at its boiling point from liquid to vapour, E = ml Unit:J/kg Experiment to find the specific latent heat of vaporisation: An electric heater is used to bring water to its boiling point. When the water boils,

the joulmeter reading (E1) and the mass of

water (m1) is recorded and then re- measured after a set time and recorded

again as (E2) and (m2) The amount of heat supplied during the recorded time interval

is = E2- E1.=E. Similarly, the

mass = m1-m2=m The equation l= is used to find 𝑬𝑬𝟐𝟐−𝑬𝑬𝟏𝟏 the specific latent heat of vaporisation. 𝟐𝟐 𝟏𝟏 ------𝒎𝒎 −𝒎𝒎

www.smarteduhub.com 5 ------NUMERICALS: ------

------

Given: l=3200J/g and mass of water= 75g Hence the amount of heat lost=E=l x m= 3200 x 75 =240 000J or 240kJ ------

------

www.smarteduhub.com 6 ------Melting and boiling point: ------Melting point: The temperature at which a substance melts is called its melting point. Boiling point: The temperature at which a substance boils is called as its boiling point. Freezing point: The temperature at which a liquid changes to a solid is called as its freezing point. ======• Whenever a substance undergoes a state change, its temperature stays the same. • The freezing point of a substance=melting point of the substance ------Energy and state change for ice:

------

www.smarteduhub.com 7 Condensation and solidification ------Condensation is when heat of vaporisation is released and the substance undergoes a state change from gas to liquid. The intermolecular forces of attraction increase and the intermolecular distance decreases and the average kinetic energy of the molecules is reduced as energy is given out.

------

Solidification is when heat of fusion is released and the substance undergoes a state change from liquid to gas. The intermolecular forces of attraction increase and the intermolecular distance decreases and the average kinetic energy of the molecules is reduced as energy is given out. ------Note: There is no change in mass during the changes of state. ------

www.smarteduhub.com 8 ------APPLICATION BASED QUESTIONS-MCQ: ------

------

www.smarteduhub.com 9 ------APPLICATION QUESTIONS-EXTENDED MCQ ------

------

www.smarteduhub.com 10 ------

------

www.smarteduhub.com 11 ------

www.smarteduhub.com 12

------

www.smarteduhub.com 13

www.smarteduhub.com 14

------

www.smarteduhub.com 15 Examples of conduction, convection and radiation: ------

Convection

------

www.smarteduhub.com 16 ------CONDUCTION CONVECTION RADIATION-MIXED BAG ------To use the following apparatus to check the emission of infra red radiations from different surfaces.

• Near the center of each side place an identical infra-red detector. • Note the temperature of each thermometer. • Then pour hot water in the box above. • Note the temperature of each thermometer after some time again for all the thermometers . • Note the rise in temperature of each thermometer. • You will find theta dull black is the best emitter. • painter shiny white is the worst emitter. ------

www.smarteduhub.com 17 ------APPLICATION BASED QUESTIONS: ------MCQ: ------

------

www.smarteduhub.com 18 ------

------

www.smarteduhub.com 19

www.smarteduhub.com 20

------

www.smarteduhub.com 21

------

www.smarteduhub.com 22 ------

------

www.smarteduhub.com 23 ------

www.smarteduhub.com 24

------