xi LIGHT 183 



20. A thick layer of a transparent liquid floats on the surface of 

 water. Trace the course of a ray of light from an object immersed 

 in the water through the floating liquid to the air. 



21. Describe and explain the effects observed when cards coloured 

 bright red, green, and blue respectively are passed from the red to 

 the blue end of the spectrum. 



22. Describe an arrangement by means of which a spectrum may 

 be formed upon a screen. 



If the light is made to fall upon a piece of red glass before reach- 

 ing the screen, how and why will the spectrum be affected ? What 

 would the effect have been if blue glass had been used ? 



