Charles Law

1
Charles Law

• Higher Physics
• Unit 1
• Mechanics and Properties of Materials

2
Introduction.

• You have just used the apparatus opposite to
  investigate the relationship between temperature
  and volume.

3
What Did You Do?

• A column of air is trapped in a capillary tube by
  a bead of mercury.
• The top end of the tube is open to the air so the
  pressure of the column of air is always equal to
  air pressure.
• As the column of air is heated the volume and
  temperature are noted.

4
Your Results (Graph 1)
5
Graph Analysis (Graph 1)

• Note the following points
• The graph is linear. Their seems to be a
  relationship between temperature and volume.
• The graph does not pass through the origin. i.e.
  Volume is not proportional to the Celcius
  temperature.
• What now?
• Redraw a graph of Volume v Kelvin Temp.

6
Volume v Temperature (Kelvin)
7
Graph Analysis

• The graph of Volume versus the Kelvin Temperature
  is straight line passing through the origin.
• The Volume is therefore directly proportional to
  the Kelvin Temperature

8
Some Maths

• V ? T (Kelvin)
• V kT
• V/T constant

9
Conclusion

• Charles Law
• The Volume of the gas is directly proportional to
  its Kelvin Temperature. (For a fixed mass of gas
  at constant pressure.)

V1 V2 T1 T2
10
Example

• A syringe has 25 ml of air trapped in it when the
  temperature is 20oC.
• Assuming the plunger of the syringe can move
  freely, what volume does the air occupy if the
  the syringe is placed in a fridge at 5oC.

11
Solution

• V1 25 ml
• T1 20oC 293K
• V2?
• T2 5oC 278K

• V1 V2
• T1 T2

• 25/293V2/278
• V2(25x278)/293
• V223.7ml