Waves · Question 47

A point source emits sound equally in all directions in a non-absorbing medium. Two points P and Q are at distances of 2 m and 3 m respectively from the source. The ratio of the intensities of the waves at P and Q is

1. 3 : 2
2. 2 : 3
3. 9 : 4
4. 4 : 9

The phase difference between two waves represented by y1 = 10-6 [100t + (x/50) + 0.5] m y2 = 10-6 [100t + (x/50)] m, where x is expressed in metres and t is expressed in seconds, is approximately

1. 1.07 radians
2. 2.07 radians
3. 0.5 radians
4. 1.5 radians

A car is moving towards a high cliff. The driver sounds a horn of frequency f. The reflected sound heard by the driver has frequency 2f. If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be

1. v/ 2
2. v/3
3. v/4
4. v/2

An observer moves towards a stationary source of sound with a speed 1/5th of the speed of sound. The wavelength and frequency of the source emitted are and f respectively. The apparent frequency and wavelength recorded by the observer are respectively

1. 1.2f, 1.2
2. 1.2f,
3. f, 1.2
4. 0.8f, 0.8

A wave travelling in positive X-direction with a = 0.2 m, velocity = 360 m s-1 and = 60 m, then correct expression for the wave is

1. y = 0.2 [2 (6t + x60 ) ]
2. y = 0.2 [ (6t + x60 ) ]
3. y = 0.2 [2 (6t - x60 ) ]
4. y = 0.2 [ (6t - x60 ) ]

A whistle revolves in a circle with angular speed = 20 rad/s using a string of length 50 cm. If the frequency of sound from the whistle is 385 Hz, then what is the minimum frequency heard by an observer which is far away from the centre (velocity of sound = 340 m/s)

1. 385 Hz
2. 374 Hz
3. 394 Hz
4. 333 Hz

The equation of a wave is represented by y = 10-4 (100t - x10 ) m, then the velocity of wave will be

1. 100 m/s
2. 4 m/s
3. 1000 m/s
4. 10 m/s

Two waves having equation x1 = a ( t - kx + 1), x2 = a ( t - kx + 2). If in the resultant wave the frequency and amplitude remain equal to amplitude of superimposing waves, the phase difference between them is

1. 6
2. 2 3
3. 4
4. 3

If the tension and diameter of a sonometer wire of fundamental frequency n is doubled and density is halved then its fundamental frequency will become

1. n4
2. 2n
3. n
4. n 2

A string is cut into three parts, having fundamental frequencies n1, n2, n3 respectively. Then original fundamental frequency n related by the expression as

1. 1n = 1n1 + 1n2 + 1n3
2. n = n1 n2 n3
3. n = n1 + n2 + n3
4. n = n1 + n2 + n33