Question

Complete the following statement. When a light source is quickly approaching you, you may perceive a:

• A. blue shift
• B. orange shift
• C. red shift
• D. violet shift
• E. green shift

Answer 1

Answer: (A)

blue shift

Let the original frequency of light source be $\nu$.

Using Doppler effect in case when the source of light moves towards the stationary observer :

Apparent frequency seen by the observer ${\nu }^{\prime }=\nu [\frac{c}{c-v_{source}}]$

$⟹$ ${\nu }^{\prime }>\nu$

Thus the observer will perceive a blue shift.