Concept First Physics and Math Learning Centre In Singapore

1.

Describe how you would demonstrate Brownian motion of smoke particles in the air. State and explain the observations.

• Direct light into the side of an enclosed smoke cell/chamber.

• View the smoke particles from the top, under a microscope.

• Bright specks of smokes will be seen as light reflects from the smoke particles

• The bright specks are observed to be in continuous random motion which proves that the smoke particles are in random motion.

• The smoke particles are in random motion because they continually bombarded unevenly on different sides by the air molecules.

2.

*Using the kinetic model of gases, explain how gases exerts a pressure on the walls of its container.

• When a gas particle collides onto the wall of the container, a force is exerted on it.

• Numerous such collisions by the many molecules results in an average force exerted on the wall.

• This force acting per unit area give rise to pressure exerted by the gas molecules on the walls of the container.

3.

*Using the kinetic model of gases, explain why the pressure exerted by a fixed mass of gas increases when its volume is reduced at constant temperature.

• When the volume is reduced, the number of particles per unit volume increases.

• Therefore, the gas particles collides more frequency with the walls, resulting in greater force exerted on the container wall.

• Since pressure P = F/A, a greater force F results in greater pressure.

4.

*Using the kinetic model of gases, explain why the pressure exerted by a fixed mass of gas increases when its temperature is raised. Assume that the volume and mass of the gas remains constant.

• When the temperature of the gas is raised, the particles have higher KE and moves faster.

• They collide with the walls of the container more vigorously and at higher frequency, resulting in greater force exerted on the container wall.

• Since pressure P = F/A, a greater force F results in greater pressure.

5.

*A gas syringe is being heated and the piston begins to be move outwards and eventually stops. Explain.

• Upon heating, the gas pressure increases to more than that of the atmospheric pressure.

• As a result, a resultant force acts outwards which pushes the piston outwards.

• As the piston moves outwards, the volume of the cylinder increases, causing the gas pressure to decrease.

• When the gas pressure drops back to a value equal to that of atmospheric pressure, there will be no more resultant outward force and the piston will stop being pushed out.