Reading Activity

Brownian motion in Liquids
Experiment; To demonstrate the Brownian motion
Apparatus: Beaker, hand lens, chalk dust, transparent lid.
PROCEDURE

Ø Sprinkle pollen grains or chalk dust on the surface of water (particles
should be small in size, light and sprinkled evenly).
Ø Cover the beaker with a transparent lid and with the help of a hand lens

BROWNIAN MOTION IN GASES
The smoke cell experiment
Experiment: To demonstrate the Brownian motion in Air
Apparatus: Drinking straw, smoke cell, microscope and a bright light source.

PROCEDURE

Trap the smoke from burning straw into the smoke cell.
Light the cell with bright light using the lens to focus the light onto the cell.
Now adjust the microscope slightly until you can see very bright specks.

See the set-up below.

Observes what happens to pollen grains or chalk dust in the first experiment, and what happen to the smoke particles in the second experiment.

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First experiment

OBSERVATION
The pollen grains or chalk dust is in constant random motion.

CONCLUSION
The particles are hit continually by the movement of small invisible particles of
water. The movement is random, suggesting that the particles of water are in
constant random movement. This kind of movement is called Brownian
motion a tribute to a scientist Robert Brown who first observed the effect.

Second Experiment

Observations and Explanation

Very bright specks are seen moving in random motion.
Bright specks are smoke particles which reflects light falling on them
The random movement of particles is due to an uneven bombardment of the smoke particles by
the invisible molecules of air. It is due to Brownian motion.
Air is made of particles which are in constant random motion.

NOTE

The microscopes magnifies the smoke particles
The light illuminates the smoke particles.

CONCLUSION

The experiments show that matter is made up of particles which in constant random motion.