Ncert Exercises & Solutions

10.14 Let us list some of the factors, which could possibly influence the speed of wave propagation:

(i) nature of the source.

(ii) the direction of propagation.

(iii) the motion of the source and/or observer.

(iv) wavelength.

(v) the intensity of the wave.

On which of these factors, if any, does

(a) the speed of light in a vacuum,

(b) the speed of light in a medium (say, glass or water), depends?

(a)
Hint: Light is an electromagnetic wave.
Step: Check the dependency of the speed of a wave on a given factor one by one.
The speed of light in a vacuum is 3 × 10⁸ m/s (approximately), which is a universal constant.
The speed of light is not get affected by the motion of the source, the observer, or both. Hence, the speed of light in a vacuum is not affected by given factors.

(b)
Hint: Light is an electromagnetic radiation.
Step: Identify the nature of light.
Light propagates in the medium as a wave, and the speed of a wave depends on the wavelengthAmong the given factors, the speed of light in a medium depends on the wavelength of light in that medium.

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