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Question

Physics Question on Waves

Radar waves are sent towards a moving airplane and the reflected waves are received. When the airplane is moving towards the radar, the wavelength of the wave

A

decrease

B

increase

C

remains the same

D

sometimes increase or decrease

Answer

decrease

Explanation

Solution

Here, vs=0v_{s}=0 and vLv_{L} is negative where vsv_{s} is velocity of source and vLv_{L} is velocity of listener (aeroplane) If apparent frequency is vv^{\prime} and vv is actual frequency, then v=v(vL)vvv^{\prime} =\frac{v-\left(-v_{L}\right)}{v} v =v+vLvv=\frac{v+v_{L}}{v} v i.e., v>vv^{\prime} > v So, apparent frequency will increase, it means apparent wavelength will decrease.