Upload
daniel-charles
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
F.4 Physics Lectures
Gas Laws
Kinetic Theory
Boyle’s LawThe 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.
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
Result
Pressure(kpa)
Volume(cm3)
1/volume(cm-3)
100120140160180200220
514338332925.523
0.0200.0230.0260.0300.0350.0390.043
pressure/kPa
1/Volume /cm-3
0.020
220
200
180
160
140
120
0.030 0.040 0.050
Graph Plotting
Conclusion
P 1/V PV = constant
P1V1 = P2V2
Boyle’s Law
Pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume
Charle’s Law
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.
Result
Length of aircolumn/cm
Temperature/K
6.06.37.07.47.78.18.9
273289308324338352373
Graph Plotting
length of air column/cm
temperature T/K
10
8
6
4
2
100 200 300 0
400
Conclusion
V T V/T = constant
V1 /T1 = V2/T2
Charle’s Law
Volume of a fixed mass of gas at constant pressure is directly proportional to its Kelvin temperature.
Pressure Law
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.
Result
Pressure P/kPa Temperature T/K94 273
100 293110 315114 333124 358128 373
Graph Plotting
pressure p/kPa
temperature T/K
10
8
6
4
2
100 200 300 0
400
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.
General Gas Equation
Boyle’s Law: PV = constant
Charle’s Law: V/T = constant
Pressure Law: P/T = constant
PV/T = constant
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.
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.
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.
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.
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.
Kinetic theory and Boyle’s 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.
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.
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.