JEE Main & Advanced Physics Thermometry, Calorimetry & Thermal Expansion Heat

(1) The form of energy which is exchanged among various bodies or system on account of temperature difference is defined as heat.

(2) We can change the temperature of a body by giving heat (temperature rises) or by removing heat (temperature falls) from body.

(3) The amount of heat (Q) is given to a body depends upon it's mass (m), change in it's temperature \[(\Delta \theta =\Delta \theta )\] and nature of material i.e. \[Q=m.c.\,\Delta \theta \]; where c = specific heat of material.

(4) Heat is a scalar quantity. It's units are joule, erg, cal, kcal etc.

(5) The calorie (cal) is defined as the amount of heat required to raise the temperature of 1 gm of water from \[{{14.5}^{o}}C\] to \[{{15.5}^{o}}C\]. Also 1 kcal = 1000 cal = 4186 J and 1 cal = 4.18 J

(6) British Thermal Unit (BTU) : One BTU is the quantity of heat required to raise the temperature of one pound (\[1\,lb\]) of water from \[{{63}^{o}}F\] to \[{{64}^{o}}F\]

1 BTU = 778 ft. lb = 252 cal = 1055 J

(7) In solids thermal energy is present in the form of kinetic energy, in liquids, in the form of translatory energy of molecules. In gas it is due to the random motion of molecules.

(8) Heat always flows from a body of higher temperature to lower temperature till their temperature becomes equal (Thermal equilibrium).

(9) The heat required for a given temperature increase depends only on how many atoms the sample contains, not on the mass of an individual atom.