Question

In Doppler effect, when a source moves towards a stationary observer, the apparent increase in frequency is due to

• A. increase in wavelength of sound received by observer
• B. decrease in wavelength of sound received by observer
• C. increase in number of waves received by observer in one second
• D. decrease in number of waves received by observer in one second

Answer 1

Answer: (B)

Change of frequency due to the Doppler effect is :
$\bar{ n }=n\left(\frac{ v }{ v - v _{ s }}\right) .$
So, $\bar{ n }> n$, So increase in the frequency.
Now, frequency is inversely proportional to the wavelength,
so in this case the wavelength will decrease.