Question

A group of students took an old shoebox and covered it with black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and making another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in Fig.2.4. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it?

(a) Explain why the milk sample was illuminated. Name the phenomenon involved.

(b) The same results were not observed with a salt solution. Explain.

(c) Can you suggest two more solutions that would show the same effect as shown by the milk solution?

Answer 1

(a) Milk is a colloidal solution hence showing the Tyndall effect.
(b) True solutions do not show the Tyndall effect because they do not scatter light.
(c) Detergent solution, sulphur solution.