F'4 Physics Lectures

1
F.4 Physics Lectures

• Gas Laws
• Kinetic Theory

2
Boyles Law
The following apparatus is used to investigate
how the pressure of a fixed mass of air varies
with its volume when the temperature is kept
constant.
3
Procedure

• Pressure is increased by applying the foot-pump
• Volume of air is read from the scale
• Pressure is measured by a Bourdon gauge
• Several pairs of readings of pressure and volume
  are taken

4
Result
5
Graph Plotting
6
Conclusion
P ? 1/V
PV constant
P1V1 P2V2
Boyles Law Pressure of a fixed mass of gas at
constant temperature is inversely proportional to
its volume
7
Charles Law
8
Procedure

• An air column is trapped in a capillary tube.
• It is heated up in a water bath in stages.
• The thermometer reading is taken.
• The length of the air column is measured.
• The reading are taken only after they have
  remained steady.

9
Result
10
Graph Plotting
11
Conclusion
V ? T
V/T constant
V1 /T1 V2/T2
Charles Law Volume of a fixed mass of gas at
constant pressure is directly proportional to its
Kelvin temperature.
12
Pressure Law
13
Procedure

• Air trapped in a flask is heated in a water bath.
• Use the thermometer and Bourdon gauge to measure
  the temperature and the pressure of the air.
• Take about several readings with different
  temperature.

14
Result
15
Graph Plotting
16
Conclusion
P ? T
P/T constant
P1 /T1 P2/T2
Pressure Law Pressure of a fixed mass of gas at
constant volume is directly proportional to its
Kelvin temperature.
17
General Gas Equation
Boyles Law PV constant
Charles Law V/T constant
Pressure Law P/T constant
PV/T constant
18
Kinetic Theory

• All matter is made up of particles, called
  molecules.
• They are constantly in motion.
• When they are close together, the molecules
  attract each other strongly.
• When they are far apart, they hardly attract each
  other.

19
Solids

• The particles are close together.
• They are held together by strong forces.
• They vibrate to and fro, but cannot change
  positions.
• They have a fixed volume and shape.

20
Liquid

• The particles are close together.
• They vibrate so vigorously that the forces can no
  longer hold them in fixed position.
• They have a fixed volume but no fixed shape.

21
Gas

• The particles are very far apart and hardly
  attract each other.
• They move at random at very high speeds.
• They have no fixed volume and shape.

22
Brownian Motion

• A smoke particle is bombarded by millions of air
  molecules around it.
• The bombardment comes from all sides but not in
  equal number.
• Brownian motion provides evidence for particle
  motion.
• This can be explained by using the kinetic theory.

23
Kinetic theory and Boyles Law

• When a gas is compressed,
• the molecules have less volume to move in.
• They hit the walls more often and so produce a
  greater pressure.

24
Kinetic theory and Charles Law

• As temperature rises, the molecules move faster
  and hit the walls more often.
• If the pressure is to remain constant, the volume
  must increase.

25
Kinetic theory and Pressure Law

• As temperature rises, the molecules move faster.
• When the volume is fixed, the molecules hit the
  walls more often.
• This increases the pressure.