Heat is a form of energy that flows from warmer to cooler bodies, with its SI unit being joules. The specific heat of a substance depends on its nature and indicates how much heat is required to raise its temperature by one degree Celsius or Kelvin. Evaporation is a cooling process where molecules escape from a liquid's surface, with its reverse process being condensation.

1. AP POLYCET 2018 STUDY MATERIAL FOR
PHYSICS(EM)
SBTET, AP, AMARAVATI

2. CHAPTER 1
HEAT
SUMMARY:
Heat is a form of energy in transit. Heat flows from a body at higher temperature to
body at lower temperature.
SI unit of heat is joule(J) and CGS unit is calorie(cal). The amount of heat required to raise
the temperature of 1 gram of water by 10
C is called calorie.
1calorie = 4.186 joule
SI unit of temperature is kelvin (K)
Relation between centigrade scale and kelvin scale of temperature:
00
C = 273K
t0
C = (273 + t)K
If two different systems A and B (thermal contact) are in thermal equilibrium independently
with another system C,
Then A and B are in thermal equilibrium with each other.
Specific heat:
The specific heat of a substance is the amount of heat required to raise the
temperature of unit mass of the substance by one degree centigrade.
CGS unit : cal/g-0
C
SI unit: J/kg-K
1 cal/g-0
C = 4.186 x 103
J/kg-K
Rise in temperature depends on the nature of the substance. Hence, Specific heat of a
substance depends on its nature.
The higher value of specific heat indicates lower the rate of rise of temperature. The
temperature and kinetic energy of the particles of the body are proportional.
Q = mS∆T or S = Q/m∆T
Where Q = quantity of required
m = mass of the substance
S = specific heat
∆T = rise in temperature

3. Method of mixtures:
Heat Lost by hot bodies = Heat gained by cold bodies.
Evaporation: The process of escaping of molecules from the surface of a liquid or the
change of phase from liquid to gas that occurs at the surface of the liquid is called
“evaporation”
Temperature falls in evaporation and takes on the surface. Hence it is a cooling process.
Rate of evaporation depends on
i) Surface area, ii) temperature, iii) amount of vapour in air.
Condensation: It is the phase change from gas to liquid.
Here temperature rises. Condensation is the reverse process of evaporation.
Humidity: The amount of water vapour present in air is called humidity.
Dew: The condensation of saturated water vapour on cold surfaces as water droplets is called
“dew”.
Fog: At low temperatures, the water molecules in large amount of vapour condense on dust
particles in air to form water droplets which float in air forming thick mist. It is called fog.
Melting: The process of converting solid into liquid is called “melting.”
The temperature of the ice does not change during melting.
Freezing: The process of converting liquid into solid is called “freezing.”
Multiple choice questions:
1. Which of the following is a warming process? [ ]
a) Boiling b) Condensation c) Evaporation d) all the above
2. Three bodies A, B and C are in thermal equilibrium. The temperature of B is 450
C,
then the temperature of C is ____________ [ ]
a) 450
C b) 500
C c)400
C d) any temperature
3.Melting is a process in which solid phase changes to __________ [ ]
a) Liquid phase b) Liquid Phase at constant temperature c) Gaseous Phase
d) Any phase
4. Specific heat S = [ ]
a) Q/Δt b) QΔt c) Q/mΔt d) mΔt/Q
5. Boiling point of water at normal atmospheric pressure is ________ [ ]
a) 0o
C b) 100o
C c) 110o
C d) -5o
C

4. 6. When ice melts, its temperature [ ]
a) remains constant b) increases c) decreases d) cannot say
7. The temperature of a steel rod is 330K. Its temperature in o
C is ______ [ ]
a) 55o
C b) 57o
C c) 59o
C d) 53o
C
8.The process of conversion of liquid into gaseous state is called_____ [ ]
a) Freezing b) Boiling c) Melting d) Fusion
9) Evaporation is called process of _____________ [ ]
a) Cooling b) Heating c) Melting d) Positive
10. When an impurity is added to a liquid, its boiling point ____________ [ ]
a) Rises b) Falls c) Remains the same d) None
11. Specific heat depends on __________________ [ ]
a) Mass b) mass, rise of temperature, and nature of material
c) Mass and nature of material d) Rise of temperature only
12. Energy of molecules in a liquid during evaporation _____________ [ ]
a) Increases b) Rises and then falls c) Decreases d) No change
13. SI unit of Specific heat is [ ]
a) J/K b) J/kg c) J/ kg-K d) J/kg/K
14. When water freezes its volume [ ]
a) Increases b) Decreases c) Remains constant d) Increases and then decreases
15. The reverse process of evaporation is [ ]
a) Condensation b) Freezing c) Melting d) oxidation
KEY
1. b 2. a 3. b 4. c 5. b 6. a 7. b 8. b 9. a
10. a 11. b 12. c 13. c 14. a 15. a

5. F