10, జులై 2016, ఆదివారం
Specific Heat – Activity:
Comparison of rate of rise in temperature of oil and water:
1. Take 800 C water in a large jar.
2. Take two test tubes, one filled with 50 g of water and other with 50 g of oil.
3. Insert two thermometers into two test tubes, with corks and place them in the hot water jar with clamp of a retort stand.
4. Observe the changes in the thermometer readings.
5. Although, the same amount of heat supplied to water and oil, we observe, the rate of rise in temperature of the oil is higher than that of the rise in temperature of the water.
6. The rate of rise in temperature depends on the nature of the substance.
Determine the components affecting the rate of rise in temperature:
a) Activity showing the rate of rise in temperature depends upon the mass of the substance:
1. Take two beakers of equal volume and take 100 grams of water in one beaker and 200 grams of water in another beaker.
2. Note down their initial temperature using thermometers.
3. Heat both beakers till the temperature of water in the two beakers rises to 600C
4. We need more time to raise the temperature of 1 Kg of water when compared with 250 grams of water.
5. That means you need to supply more heat energy to greater quantity of water than lesser quantity of water to attain same temperature.
6. For same change in temperature the amount of heat (Q) absorbed by a substance is directly proportional to its mass (m).
=> Q α m (when ΔT is constant)
b. Activity showing the rate of rise in temperature depends upon the amount of heat (Q) absorbed by the substance:
1. Take 1 liter of water in a beaker and heat it over a constant flame.
2. Note the temperature changes (ΔT) for every two minutes.
3. We will notice that the temperature rise with time in constant proportions.
4. That means, for the same mass (m) of water the change in temperature is proportional to the amount of heat (Q) absorbed by the substance.
=> Q α ΔT.
Derivation of Equation for specific heat (S):
1. For same change in temperature the amount of heat (Q) absorbed by a substance is directly proportion to its mass (m).
=> Q α m - - - - - - - - - - I
2. For same mass (m) of water the change in temperature is proportional to the amount of heat (Q) absorbed by it.
=> Q α ΔT - - - - - - - - - - II
3. From the above I, II equations, we get
=> Q α m ΔT
=> Q = m S ΔT
4. The Constant ‘S’ in the above equation is called ‘Specific heat’ of the substance.
Specific Heat – Definition:
The specific heat of substance is the amount of heat required to raise the temperature of unit mass of the substance by one unit. It is represented by ‘S’.
Specific heat units:
C.G.S system: cal/g 0C
S.I System: J/Kg.K
1 cal/g 0C = 4.2x103 J/Kg.K