Question

The students in a class took a thick sheet of cardboard and made a small hole in its centre. Sunlight was allowed to fall on this small hole and they obtained a narrow beam of white light. A glass prism was taken and this white light was allowed to fall on one of its faces. The prism was turned slowly until the light that comes out of the opposite face of the prism appeared on the nearby screen. They studied this beautiful band of light and concluded that it is a spectrum of white light.

1. Give any one more instance in which this type of spectrum is observed.    (1)
2. What happens to white light in the above case?    (1)
3. 1. List two conditions necessary to observe a rainbow.   (2)
      OR
   2. Draw a ray diagram to show the formation of a rainbow. Mark on it points (a), (b) and (c) as given below:   (2)
      1. Where dispersion of light occurs.
      2. Where light gets reflected internally.
      3. Where final refraction occurs.

Answer 1

i. Example of a rainbow is when white light travels through a raindrop.

ii. White light experiences refraction at both interfaces as it travels through a glass prism, dispersing into its component colors. Spectrum is created when distinct colors of light bend at different angles because of their different wavelengths.

iii. A.

1. Sunlight must enter the droplet.
2. The observer needs to be positioned between the raindrop and the sun.

OR

B.