Q. Radar waves are sent towards a moving aeroplane and the reflected wave are received. When the aeroplane is moving towards the radar, the wavelength of the wave
A) Decreases
B) Increases
C) Remains the same
D) Sometimes increases or decreases
Explanation
(a) Here, $v_{s} = 0\ and\ v_{L}$ is negative where $v_{s}$is velocity of source and $v_{L}$is velocity of listener (aeroplane)
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If apparent frequency is v’ and v is actual frequency, then
$v^{''} = \frac{v - \left( - v_{L} \right)}{v}v = \frac{v + v_{L}}{v}L$
$i.e.,$ v’>v
So, apparent frequency will increase, it means apparent wavelength will decrease.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.