SS2 Second Term Physics Lesson Note – Heat Energy III

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WEEK 8

TOPIC: HEAT ENERGY

CONTENT:

• Determination of specific heat capacity of liquid.
• Latent heat
• Determination of specific latent heat of fusion of ice.
• Determination of specific latent heat of vaporization of steam.

SUB-TOPIC 1: Determination of specific heat capacity of liquid by electrical method.

Apparatus: Thermometer, liquid, calorimeter, heater, stop clock, chemical/ beam balance

Diagram:

Method:

A calorimeter of known heat capacity (M_cC_c) is used and a known mass of liquid( M₁)  is placed in the calorimeter, the temperature of the liquid is recorded (θ₁₎). The known quantity of heat (VIt) is recorded by taking readings from the voltmeter, ammeter and stop watch. The final temperature is recorded (θ₂).

Calculations:

Electrical energy supplied by the heater = Heat energy absorbed by the calorimeter and water.

VIt  = M₁C_L(θ₂ – θ₁)  +  M_cC_c (θ₂ –θ₁)

 

C_L =  VIt –  M_c C_c (0₂ – 0₁)

C₁  (0₂ – 0₁)

LATENT HEAT

Latent heat or hidden heat is experienced when there is a change of state ( melting, vaporization, condensation, freezing, sublimation), it is not visible in the thermometer because there is no change in temperature. There are latent heat of fusion and latent heat of vaporization.

Latent heat of fusion is the heat energy required to convert a substance from its solid form to its liquid form without change in temperature.

Specific latent heat of fusion of a substance is the quantity of heat required to change unit mass of a substance from solid to liquid without change in temperature. The unit is Jkg^-1.

Q = quantity of heat(in joules)

m = mass of substance(kg)

Q = ml

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