Level 2

For an electromagnetic wave, which of the following statements is true?

Two sources $\mathrm{A}$ and $\mathrm{B}$ are sounding notes of frequency $680 \mathrm{Hz}.$A listener moves from $\mathrm{A}$ to $\mathrm{B}$ with a constant velocity u. If the speed of sound is $340 \mathrm{m}/\mathrm{s},$ what must be the value of $\mathrm{u}$ so that he hears 10 beats per sec ?

A source of sound emitting a note of frequency $200 \mathrm{Hz}$ moves towards an observer with a velocity $v$ equal to the velocity of sound. If the observer also moves away from the source with the same velocity $v,$ the apparent frequency heard by the observer is

A train whistling at constant frequency $n$ is moving towards a station at a constant speed $V$, then train goes past a stationary observer on the station. The frequency $n$ of the sound as heard by the observer is plotted as a function of time $t$. Identify the correct curve.

The apparent change in frequency of sound due to the relative motion between the observer and the source of sound is called

Three sinusoidal waves with the same angular frequency but with different amplitudes $A, \frac{A}{2}, \frac{A}{3}$ and phase angles $0, \frac{\pi }{2}$ and $\pi$ respectively move along the same direction and superpose with each other. The amplitude of the resultant wave is given by

A source of sound gives $5$ beats per second when sounded with another source of frequency $100 {\mathrm{s}}^{-1}.$ The second harmonic of the source together with a source of frequency $205 {\mathrm{s}}^{-1}$ gives $5$ beats per second. The frequency of the source is

In a standing wave on a string rigidly fixed at both ends: