A clock with a luminous dial is moving toward an observer at a speed that is a large fraction of the speed of light. Which of these will the observer measure?
A) The light emitted by the clock will be shifted toward longer wavelengths compared to those seen by an observer moving with the clock.
B) The light from the clock is approaching the observer at speed c.
C) The clock runs fast compared to an identical clock at rest in the observer's hand.
D) The clock appears thicker, front to back, than the identical clock in observer's hand.

Question

Quizplus · Accepted Answer

The speed of light in a vacuum is constant and does not change regardless of the relative motion of the source and the observer. This principle is a cornerstone of Einstein's theory of relativity, indicating that the light from the clock approaches the observer at speed c, the speed of light in a vacuum.

A Clock with a Luminous Dial Is Moving Toward an Observer