Specific Heat Capacity

Heat is the most common form of energy. Heat can be transferred from one place to another by means of conduction, convection and radiation. It can be converted into other forms of energy.

Sun is the main source of heat energy for Earth. Fuels such as wood, petrol, coal and gas are other sources of heat energy. For the survival of all living things, heat energy is essential.

The temperature of a body is a measure of its hotness or coldness. It is a measure of the kinetic energy of the particles of the body.

Change in temperature, change of state and thermal expansion in a body, are some of the main observable physical effects of heat energy. Heat energy plays a major role in determining the climatic and weather conditions.

Specific Heat Capacity

We take three identical glass beakers and fill them with equal mass of water, kerosene and coconut oil. We first note down their initial temperatures and then heat them one by one by same lamp for 5 minutes each; we find that the rise in temperature of each of them is different.

We take four cylindrical blocks of aluminium, lead, copper and iron of equal mass having the same area of cross section. Now, we suspend the cylindrical blocks fully inside boiling water. After few minutes, take out the blocks simultaneously and place them on a thick paraffin cake side by side. What we observe is that depths of sink are different for different materials.

We take a stone and water of same mass. Place them in the hot sun for about half an hour. Now touch the stone with one hand and water with the other hand. What we observe is that the stone is hotter than water.

When a substance is heated, it absorbs heat energy and its temperature rises. The amount of heat energy absorbed by the substance (Q) is directly proportional to mass of the substance (m) and the change in temperature (Δt)

Q = m sΔt

Here s is a constant called Specific Heat Capacity. The value of the specific heat capacity depends on the nature of the substance. In the above equation, If m = 1 kg and Δt = 1 K then Q = s. This implies that:

The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of 1 kg mass of the substance by 1 K. Its unit is J kg^-1 K^-1. It is a measure of thermal inertia of a substance.

The heat capacity of a substance is defined as the amount of heat required to raise the temperature of the substance through 1 K.

Thus:

Heat capacity = mass x specific heat capacity.

Its unit is J/K.

The following table shows the specific Heat Capacity of some common materials.

Among the liquids, the specific heat capacity is maximum for water, hence water is used as a coolant in radiators of automobile engines and mercury is used as a thermometric liquid.