question_answer

Radar waves are sent towards a moving aeroplane and the reflected waves 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 .

Correct Answer: A

Solution :

Here, \[{{v}_{s}}=0\] and \[{{v}_{L}}\] is negative where \[{{v}_{s}}\] is velocity of source and \[{{v}_{L}}\] is velocity of listener (aeroplane) If apparent frequency is v and v is actual frequency, then \[v=\frac{v-(-{{v}_{L}})}{v}v\] \[=\frac{v+{{v}_{L}}}{v}v\] i.e., \[v>v\] So, apparent frequency will increase, it means apparent wavelength will decrease.