Question

A pilot of a spaceship travelling at 90% the speed of light turns on the ship's laser headlights just as it passes a stationary observer. Identify which of the following statements is true according to doppler effect of light?

• A. The pilot will measure the speed of the light coming out of the headlights as c, and the observer will measure the speed of the light as 0.9c.
• B. The pilot will measure the speed of the light coming out of the headlights as c, and the observer will measure the speed of the light as 1.9c.
• C. The pilot will measure the speed of the light coming out of the headlights as 0.9c, and the observer will measure the speed of the light as 1.9c.
• D. The pilot will measure the speed of the light coming out of the headlights as 1.9c, and the observer will measure the speed of the light as 0.9c.
• E. The pilot will measure the speed of the light coming out of the headlights as c, and the observer will measure the speed of the light as c.

Answer 1

The correct option is E The pilot will measure the speed of the light coming out of the headlights as c, and the observer will measure the speed of the light as c.

According to Einstein's special theory of relativity, light travels with a constant speed equal to $c$ in all the inertial frames.

Thus the pilot will measures the speed of the light coming out of the headlights as c and the observer will measure the speed of light as c.