An earth satellite has a velocity component of 7 km/s towards an earth observer. It emits a signal of frequency 100 MHz. This is combined with a signal of same frequency produced by a local oscillator. The approximate beat frequency (in Hz) will be:


Correct option is



The velocity of a satellite is small compared to the velocity of light (e.m. signal wave). Hence, using the simplified formula for the apparent change of frequency due to Doppler’s effect,



c = 3 × 105 km/s, gives df = 2400 = no. of beats per second.



In a good tuning fork:


A flat horizontal platform moves up and down in SHM with an amplitude of 1 cm. A small object is placed on the platform. What is the maximum frequency the platform can have, if the object is not to separate from it during any part of motion?


When a tuning fork is vibrating, the vibrations of the two prongs:


One of the prongs of a tuning fork is broken. The intensity of sound produced by it will:


A sound wave of wavelength λ travels towards the right horizontally with a velocity v. It strikes and reflects from a vertical plane surface, travelling at a speed v towards the left. The number of positive crests striking in a time interval of three seconds on the wall is:


A tuning fork is set into vibrations and then it is held with its stem resting on a table. How will the duration of its vibrations be affected?


S1 and S2 are two stationary sources of sound, of frequencies 320 Hz and 324 Hz respectively, placed at a good distance from each other. The velocity with which an observer should walk towards S1 along the line joining S1 and S2 in order that he may hear no beats, is about (velocity of sound = 332 ms–1):


Which of the following emits a pure sine wave?


The air column inside a sonometer is in resonance with a tuning fork placed on the wooden board. If the wooden board is now evacuated, check the correct statement: