121.

The tension of a stretched string is increased by 69 %. In order to keep its frequency of vibration constant, its length must be increased by

• 30 %

• 20 %

• 69 %

• $\sqrt{69} \%$

Under the same conditions of temperature and presssure, the velocity of sound in oxygen and hydrogen are v_o and v_H. Then

• v_o = 4v_H

• v_H = 4v_o

• v_o = v_H

• v_H = 16v_o

Forty one tuning forks are arranged in increasing order of frequencies such that every fork gives 5 beats with the next. The last fork has a frequency that is double the frequency of the first fork is

• 210

• 400

• 205

• 200

In a stationary wave all the particles

• in the region between two nodes vibrate in same phase

• on either side of a node vibrate in same phase

• of the medium vibrate in same phase

• in the region between two antinodes vibrate in same phase

A cylindrical tube open at both ends, has a fundamental frequency f₀ in air. The tube is dipped vertically into water such that half of its length is inside water. The fundamental frequency of the air column now is

• f₀

• $\frac{3{\mathrm{f}}_0}{4}$

• 2f₀

• $\frac{{\mathrm{f}}_0}{2}$

A man x can hear upto 10 kHz and another man y upto 2 kHz. A note of frequency 500 Hz is produced before them from a stretched string then both will hear sounds of

• different pitch but same quality

• same pitch but different quality

• same pitch and same quality

• different pitch and different quality

The equation $\mathrm{y} = \mathrm{A} {\cos }^2 \left[2\mathrm{\pi nt} - 2\mathrm{\pi }\frac{\mathrm{x}}{\mathrm{y}}\right]$ represents a wave with

• amplitude A/2, frequency 2n and wavelength λ

• amplitude A/2, frequency 2n and wavelength $\frac{\mathrm{\lambda }}{2}$

• amplitude A, frequency n and wavelength λ

• amplitude A, frequency 2n, wavelength 2λ

A light points fixed to one prong of a tuning fork touches a vertical plate. The fork is set vibrating and the plate is allowed to fall freely. If eight oscillations are counted when the plate falls through 10 cm, the frequency of the tuning fork is

• 280 Hz

• 360 Hz

• 56 Hz

• 560 Hz

Out of the following options which one can be used to produce a propagating electromagnetic wave?

• A stationary charge

• A chargeless particle

• An accelerating charge

• An accelerating charge

A train moving t a speed of 220 ms^-1 towards a stationary object. emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is
(speed of sound in air is 330 ms^-1)

• 3500 Hz

• 4000 Hz

• 5000 Hz

• 5000 Hz