With what velocity should an observer approach a stationary sound source, so that the apparent frequency of sound should appear double the actual frequency? (v is velocity of sound).

• $\frac{\mathrm{v}}{2}$

• 3v

• 2v

• v

A string vibrates with a frequency of 200 Hz. When its length is doubled and tension is altered, it begins to vibrate with a frequency of 300 Hz. The ratio of the new tension to the original tension is

• 9 : 1

• 1 : 9

• 3 : 1

• 1 : 3

How many times more intense is a 60 dB sound than a 30 dB sound ?

• 1000

• 2

• 100

• 4

94.

Two sources are said to be coherent if they produce waves

• having a constant phase difference

• of equal wavelength

• of equal speed

• having same shape of wavefront

According to Newton's corpuscular theory, the speed of light is

• same in all the media

• lesser in rarer medium

• lesser in denser medium

• independent of the medium

Sound waves transfer

• only energy not momentum

• energy

• momentum

• Both (a) and (b)

A stationary point source of sound emits sound uniformly in all directions in a non-absorbing medium. Two points P and Q are at a distance of 4 m and 9 m respectively from the source. The ratio of amplitudes of the waves at P and Q is

• $\frac{3}{2}$

• $\frac{4}{9}$

• $\frac{2}{3}$

• $\frac{9}{4}$

$\mathrm{y} = 3 \sin \mathrm{\pi }\mathrm{ }\left(\frac{\mathrm{t}}{2} - \frac{\mathrm{x}}{4}\right)$ represents an equation of a progressive wave, where t is in second and x is in metre. The distance travelled by the wave in 5 s is

• 8 m

• 10 m

• 5 m

• 32 m

A cylindrical tube open at both the ends has a fundamental frequency of 390 Hz in air. If $\frac{1}{4}$th of the tube is immersed vertically in water the fundamental frequency of air column is

• 260 Hz

• 130 Hz

• 390 Hz

• 520 Hz

A bat flies at a steady speed of 4 ms^-1 emitting a sound of f =90 x 10³  Hz. It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (take velocity of sound in air is 330 ms^-1)

• 88.1 × 10³ Hz

• 87.1 × 10³ Hz

• 92.1 × 10³ Hz

• 89.1 × 10³ Hz