In a wave motion y = A sin (kx - ωt), y can represent

• electric field

• magnetic field

• displacement

• pressure

A stationary source emits a sound moving towards a wall with a velocity u. Speed of sound in air is v. The fractional change in the wavelength of the sound sent and the reflected sound is

• $\frac{\mathrm{v} + \mathrm{u}}{\mathrm{v} - \mathrm{u}}$

• $\frac{2\mathrm{u}}{\mathrm{v} + \mathrm{u}}$

• $\frac{2\mathrm{v}}{\mathrm{v} + \mathrm{u}}$

• $\frac{\mathrm{u} + \mathrm{v}}{2\mathrm{v}}$

Two sound waves with wavelengths 4 m and 5 m respectively each propagating in a gas with velocity 340 m/s. The number of beats per second will be

• 12 Hz

• 15 Hz

• 17 Hz

• 11 Hz

Two tunning forks A and B, produce notes of frequencies 258 Hz and 262 Hz. An unknown note sounded with A produces certain beats. When the same note is sounded with B. The beat frequency gets doubled. The unknown frequency is

• 250 Hz

• 252 Hz

• 254 Hz

• 256 Hz

A bat emitting an ultrasonic wave of frequency 2 x 10⁴ Hz flies at a speed of 6 m/s between two parallel walls. The beat frequency between the two frequencies heard
by the bat is (Given, speed of sound is 330 m/s)

• 600 Hz

• 800 Hz

• 900 Hz

• 1300 Hz

The equation of a simple harmonic wave is given by y = 3sin $\frac{\mathrm{\pi }}{2}$ (50 t - x) where, x and y are in meters and t in seconds. The ratio of maximum particle velocity to the wave velocity is 

• 2$\mathrm{\pi }$

• $\frac{3}{2}\mathrm{\pi }$

• $3\mathrm{\pi }$

• $\frac{2}{3}\mathrm{\pi }$

257.

Two strings with mass per unit length of 9 gcm^-1 and 25 gcm^-1 are joined together in series. The reflection coefficient for the vibration waves are

• $\frac{9}{25}$

• $\frac{3}{5}$

• $\frac{1}{16}$

• $\frac{9}{16}$

The equation of a wave is y = 5 sin $\left(\frac{\mathrm{t}}{0.04} - \frac{\mathrm{x}}{4}\right)$ where x is in cm and t in seconds. The maximum velocity of the wave will be

• 1 ms^-1

• 2 ms^-1

• 1.5 ms^-1

• 1.25 ms^-1

When the two waves y₁ = a sin ωt and y₂ = a cos ωt are superimposed, then resultant amplitude is

• a

• 2a

• $\sqrt{2}\mathrm{a}$

• $\frac{\mathrm{a}}{\sqrt{2}}$

A train moves towards a stationary observer with speed 34 ms^-1 . The train sounds a whistle and its frequency registered by the observer is v₁ , If the train's speed is reduced to 17 ms^-1, the frequency registered is v₂.  If the speed of sound is 340 ms^-1 , then the ratio v₁ /v₂ is

• 2

• $\frac{1}{2}$

• $\frac{18}{19}$

• $\frac{19}{18}$