Which of the following are true?
A. Speed of light in vacuum is dependent on the direction of propagation.
B. Speed of light in a medium is independent of the wavelength of light.
C. The speed of light is independent of the motion of the source.
D. The speed of light in a medium is independent of intensity.
Choose the correct answer from the options given below:

Solution

Physics sir · 3 steps

In vacuum, light's speed is the same for everyone; only a medium makes it depend on wavelength.

1. In vacuum. Light travels at c = 3 × 10⁸ m s⁻¹ in every direction, and this value does not change with the motion of the source. So A is false and C is true.
2. In a medium. Speed in a medium is v = c/n, and the refractive index n changes with wavelength. That is dispersion, the reason a prism splits white light, so B is false.

   Statement	True or false	Reason
   A	False	c is the same in all directions in vacuum
   B	False	n depends on λ, so v does too
   C	True	c does not depend on the motion of the source
   D	True	Brighter light has a larger amplitude, but its speed stays c/n

3. So. Only C and D are true, which is option (d).

The idea to keep. Speed of light depends on the medium and, inside a medium, on wavelength. It never depends on direction in vacuum, on the source's motion, or on how bright the light is.

Answer from the NTA final answer key. Solution by PrepWiser.