Question

Water waves are moving towards a man at a speed of $10m/s$ and frequency of $2Hz$. The man is sitting in a rowboat offshore. Which of the following properties of the waves seen by the child would be greater when the boat is moving away from the beach than when the boat is stationary with respect to the beach?

I. Speed of the waves with respect to the boat
II. Frequency of the waves
III. Wavelength of the waves

• A. I only
• B. III only
• C. I and II only
• D. II and III only
• E. I, II, and III

Answer 1

The correct option is C I and II only

According to Doppler effect, the relative speed of the waves change when the observer or source moves. Wavelength of the waves doesn't change because the distance doesn't depend on the reference frame. Frequency also changes as speed = wavelength X frequency.