alevel物理A2 expts thermal

A2 / Yr 13 Experiments – Thermal Physics

Smoke particles observed under a microscope can be

seen to move randomly. This Brownian motion can

also be observed in pollen grains in water

The specific heat capacity of a metal block or a liquid can be determined by measuring the electrical energy input (voltage x current x time) and dividing this by the mass and temperature rise of the sample.

Note – the temperature may continue to

rise for a few minutes after the heater is

switched off. Also the value for the SHC

will be an overestimate because some

heat is lost to the surroundings even with the insulation lagging

The specific heat capacity can also be determined using the

method of mixtures in which a known mass of metal heated to temperature T1 is immersed in water of temperature T2 and the final temperature of this metal and water system T3 is measured

SHC metal = (mass of water x 4180J/kg/K x T3-T2) ÷ (mass of metal x T1-t3)

A similar experiment can be conducted using the heater to melt ice at 0o C. The electrical energy supplied (voltage x current x time) divided by the mass of ice that

melted due

to the

heating is

the specific

latent heat

of fusion of ice. It is important that a fine

gauze or similar is at the base of the funnel to

stop smaller chunks of ice from falling

through. It is also important to measure how much ice would melt naturally during the experiment as a control and remove this value from the amount recorded from the experiment

A similar experiment can be used to determine the specific latent heat of vaporization from input energy divided by the mass of water evaporated at 100o C. Both of these experiments should be conducted with water as close to the change of state temperature as possible and both will be over estimates due to the heat loss to the surroundings

Gas Law experiments:

1.Boyle’s Law – PV is constant can be explored by pumping

an oil up a tube and recording the pressure and the

reduced volume of the air in the tube. Plotting 1/V

against pressure should give a straight line graph

providing that the temperature does

not change

2.Charles’ law – VαT can be

investigated using a capillary tube

containing one end plugged with oil and sulphuric acid. If

the glass tube is heated and the tube is open at end then

the pressure should be constant and measurements of

temperature and volume should enable a straight line graph to be produced 3.The Gas Law (sometimes know as Gay-Lussac’s law) – PαT can be

investigated using a flask of air attached to a

Bourdon gauge which is heated or cooled using

a water bath. Since the volume is constant

measurements of temperature and volume

should enable a straight line graph to be

produced