Question

In an experiment, Pooja used an equilateral triangular glass prism and projected a narrow beam of white light source from one side of the surface of the prism. She placed a screen on the other side and saw many colours appearing as patches on the screen. But when she used a red-light source, she could only see a red patch on the screen. Similarly, she used a blue and green light source and could only see one colour patch on both occasions.
(i) The phenomenon that she was trying to demonstrate was:
A. Dispersion
B. Reflection
C. Refraction
D. Scattering

(ii) The reason why she could not see any other colour when the red light was used was because:
A. Red colour does not refract in prism.
B. Red colour is monochromatic.
C. The prism was defective.
D. The prism is opaque to red colour

(iii) Which of the following can be the correct explanation that Pooja can give to her friends to explain this phenomenon?
A. Different lights travel faster in the glass prism at different rates.
B. Any light would disperse in the prism.
C. Enough data is not available to make a scientific explanation in this case.
D. Different wavelengths travel at different speeds in the glass

(iv) She also could relate to another natural phenomenon that we observe on a rainy humid day as the sun comes out. What could be that phenomenon?
A. Lightning.
B. Blueness of the sky.
C. Rainbow.
D. Scattering of light

Answer 1

The separation of visible light into its different constituent colors is known as Dispersion of light.

Explanation:

• Pooja used a glass prism to obtain different colors from a single light source which is known as dispersion.

Therefore, The phenomenon that she was trying to demonstrate was (A) Dispersion.

• Monochromatic colors are those colors of a single hue. Scientifically, they are of single wavelength or frequency. Red is one of the monochromatic colors.

Hence, The reason why Pooja could not see any other color when the red light was used was because (B) Red colour is monochromatic.

• A white light consists of several wavelengths of light which makes them travel at different speeds (except vacuum) in any medium for example glass.

Hence, The correct explanation that Pooja can give to her friends to explain this phenomenon is (D) Different wavelengths travel at different speeds in the glass.

• When the sun shines on rain drops, a rainbow appears in the sky as a natural spectrum of sunlight in the form of bows. In the atmosphere, it is the result of sunlight reflection, refraction, and dispersion from water droplets.

Therefore, The Natural Phenomenon that we observe on a rainy humid day as the sun comes out is (C) Rainbow.

Answer 2

Explanation:

(I) dispersion

(ii) red colour is monochromatic

(oii) different wavelengths travel at different speeds in glass

(iv) rainboe