Preparation and setup

1. Boil a kettle of water and pour into the tall form beaker placed on the heatproof mat

2. Place the Charles Law tube into the beaker sealed end first and leave to heat.

3. Pour some oil into the 250ml beaker

4. Carefully invert the Charles Law tube into the oil, as it cools it will draw the oil into the tube. 1cm of oil will be sufficient.

5. Pour out the water from the tall form beaker

6. Lift the tube, wipe the excess oil off with the paper towel and invert it back into the tall form beaker.

7. Take the strand of wire, bend the end of the wire so it won’t fall down the tube.

8. By placing some of the wire into the tube, carefully use the wire to set the oil bead halfway down the tube.
    

Conducting the Experiment

1. Pour hot water from a slightly cooled kettle into the beaker

2. Stir the water well using the thermometer, read the value of its temperature, θ, and the length of the air sample, l, on the 30 cm ruler.

3. Allow the water to cool by 5 °C and repeat the procedure until room temperature has been reached. (The cooling process can be speeded up by pouring a little water out of the beaker and topping it up with cold water.)

Charles’s Law

Calculations and Analysis

1. Plot a graph of l against θ. Start the axes at a convenient value, and use a scale which will give a spread of points over at least half the graph paper in both directions.

2. Draw the best straight line of fit though the points and find the gradient, m.

3. The form of the graph is l = mθ + c, where c is the value of l when θ = 0 °C.

4. The value of c can be found by reading a pair of values for length and temperature for a point on the straight line (_l_1 and θ1, say). Then c = l1 - mθ1.

5. An estimate of the value of absolute zero, θ0, can then be found by substituting l = 0 into the equation for the form of the graph: 0 = mθ0 + c so θ0 = -c/m.