Question 161: Waves

Question

An observer is moving with half the speed of light towards a stationary microwave source emitting waves
at frequency 10 GHz. What is the frequency of the microwave measured by the observer? (speed of light =
3 ×10
8
ms
–1
)

Accepted Answer

This question is from Doppler's effect of light.
When observer is moving towards the source then the frequency of wave measured by the observer will be
f
observed
= f
actual
$$\sqrt {{{c + v} \over {c - v}}} $$
where c = speed of light and v = speed of observer
According to the question, v = $${c \over 2}$$
$$	herefore$$ f
observed
= f
actual
$$\sqrt {{{c + {c \over 2}} \over {c - {c \over 2}}}} $$
= 10$$ 	imes $$$$\sqrt {{{{{3c} \over 2}} \over {{c \over 2}}}} $$
= 10$$\sqrt 3 $$ = 17.3 GHz

Answer

15.3 GHz

Answer

10.1 GHz

Answer

12.1 GHz

Answer

17.3 GHz

Waves

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer? (speed of light = 3 ×10 8 ms –1 )

Choose the correct answer: