Thermal Capacity

Thermal Capacity

Thermal Capacity of a substance is defined as the amount of heat required to change its temperature through one degree. If Q is the amount of required to change the temperature of a body of mass m through, then Q = msΔθ

If temperature difference = 1, then

Q = ms

The value of thermal capacity of a body depends upon the nature of the body and it’s mass.

Dimension: [ML²T¯²θ¯¹], Unit: J/ K

If a mass of a body which absorbs or emit the same degree rise of fall in temperatures, suppose m is the mass of the body which required Q amount of heat to raise the temperature by θ.

If S is the specific heat capacity of the body then, Q = msΔθ … (1)

If w is water equivalent of the body, sw is specific heat capacity of the water. Then, from the definition of water equivalent:

Q = wswΔθ … (2)

Comparing equations (1) and (2) we get:

wswΔθ = msΔθ

wsw = ms ⇒ $$w=\frac{ms}{{{s}_{w}}}$$,

In CGS system, specific heat capacity of water, sw = 1 cal/g.C

Then, w = ms

So, the water equivalent of a substance is normally equal to its thermal capacity in CGS system, but the unit of water equivalent is grams and that of thermal capacity is calories.