A signal of 5 kHz frequency modulates a carrier of frequency 1 MHz and peak voltage 25 V. If the amplitude at the sidebands of the amplitude modulated signal is 5 V, then the modulation index is

• 0.8

• 0.6

• 0.4

• 0.2

If a closed organ pipe of length L₁ in its fundamental mode resonates with an open organ pipe of length L₂ then L₁ : L₂ is

• 1 : 2

• 2 : 1

• 1 : 4

• 4 : 1

The physical quantity that remains unchanged when a sound wave goes from one medium to another is

• amplitude

• speed

• wavelength

• frequency

The beat frequency observed when two sound waves y₁ = 0.5 sin (410 t) and y₂ = 0.5 sin ( 454 t) travel in the same direction is

• 5

• 3

• 7

• 2

Tube A has both ends open while tube B has one end closed. Otherwise they are identical. Their fundamental frequencies are in the ratio

• 4 : 1

• 2 : 1

• 1 : 4

• 1 : 2

The speed of sound in a gas of density ρ at a pressure p is proportional to

• ${\left(\frac{\mathrm{p}}{\mathrm{\rho }}\right)}^2$

• ${\left(\frac{\mathrm{p}}{\mathrm{\rho }}\right)}^{3/2}$

• $\sqrt{\frac{\mathrm{\rho }}{\mathrm{p}}}$

• $\sqrt{\frac{\mathrm{p}}{\mathrm{\rho }}}$

A tuning fork of frequency 330 Hz resonates with an air column of length 120 cm in a cylindrical tube, in the fundamental mode. When water is slowly poured in it, the minimum height of water required for observing resonance once again is (Velocity of sound 330 ms^-1)

• 75 cm

• 60 cm

• 45 cm

• 30 cm

If the frequency of human heart beat is 1.25 Hz, the number of heart beats in 1 min is

• 80

• 65

• 90

• 75

39.

Velocity of sound in air is 320 ms^-1. A pipe closed at one end has a length of 1 m. Neglecting end correction, the air column in the pipe cannot resonate with sound of frequency

• 80 Hz

• 240 Hz

• 320 Hz

• 400 Hz

A whistle is blown from the tower of a factory with a frequency of 220 Hz. The apparent frequency of sound heard by a worker moving towards the factory with a velocity of 30 ms^-1 is (velocity of sound = 330 ms^-1)

• 280 Hz

• 200 Hz

• 300 Hz

• 240 Hz