

Explanation
(a)(i) Temperature is a number which expresses how hot or cold a body is on scale such as centigrade orkelvin. S.I. unit is kelvin (K). Temperature decides which direction heat will flow while, heat is a form of energy S.I. is Joules (J).
(ii) Two physical properties used for measuring temperature are:- (1) Change in volume of liquid with temperature (2) Change in resistance. Others are: (3) Expansion of solids (4) Expansion of volumeof gas.
(b)(i) Determination of the upper - fixed point for a mercury-in-glass thermometer.

To determine the upper fixed point, a hypsometer is used. The experiment is set up as shown above. The manometer is used to measure the pressure of the steam.
If it is not 76cm Hg, an adjustment is made to the upper fixed point. When the mercury level is constant, a mark is made on its glass to fix the point. One precaution that must be observed in this experiment is that the thermometer must not touch the water, because its temperature is affected by dissolved impurities in the water.
(ii) The constant - volume gas thermometer measures temperature more accurately than other thermometers because its glass expansion is negligible compared to the expansion of the gas. It is seldom used as everyday laboratory thermometer because it is not easily handled unlike the laboratory thermometer.
(c) In the kinetic theory, molecules are in random motion. They all have different velocities. Near the surface, some liquid molecules with high velocities in an upward direction may have sufficient kinetic energy to break through the surface. Then they become molecules of vapour. The average kinetic energy ofthe liquid remaining is therefore reduced, and so its temperature is lowered.

