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CGPET 2015 Solved Paper

Section: Physics

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Question : 6 of 150

Marks: +1, -0

If an observer moves towards stationary source, then the apparent frequency is given by

$f' = f \left(\frac{v+v_0}{v}\right)$
$f' = f \left(\frac{v v_0}{v}\right)$
$f' = f \left(\frac{v}{v+v_0}\right)$
$f' = f \left(\frac{v}{v-v_0}\right)$

Solution:

Generalised formula for apparent frequency is

f_a = \left(\frac{v \pm v_0}{v \mp v_s}\right) f_0

According to the question source is stationary,

v_s = 0

f_a = f' = \left(\frac{v \pm v_0}{v}\right) f_0

Observer is moving towards the source

\Rightarrow f_a = f' \left(\frac{v + v_0}{v}\right) f

where, v = speed of the wave

v_0

= speed of the observer

f = original frequency of the source

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