Bubbles of air coming out through water in glass vessel appears silvery to an observer standing by the sides Explain the reason.

• Take a thick sheet of cardboard and make a small hole or narrow slit in its middle. • Allow sunlight to fall on the narrow slit. This gives a narrow beam of white light. • Now, take a glass prism and allow the light from the slit to fall on one of its faces as shown in Fig. • Turn the prism slowly until the light that comes out of it appears on a nearby screen. What do you observe? You will find a beautiful band of colours.

Take a table - tennis ball and make three slits into it. put semicircular fins cut out of a metal sheet into these slits. Pivot the tennis ball on an axle through its centre with a straight metal wire fixed to a rigid support. Now connect a cycle dynamo to this. connect a bulb in series. Direct a jet of water or steam produced in a pressure cooker at the fins. What do you observe ?

Explain why Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)