JEE Physics Waves MCQs Set B

Question. In a closed organ pipe of length 105 cm, standing waves are set up corresponding to third overtone. What distance from the closed end, a pressure node is formed?
(a) 15 cm
(b) 25 cm
(c) 30 cm
(d) 5 cm

Answer: D

Question. A uniform string resonates with a tuning fork, at a maximum tension of 32 N. If it is divided into two segments by placing a wedge at a distance one-fourth of length from one end, then to resonance with same frequency the maximum value of tension for string will be
(a) 2 N
(b) 4 N
(c) 8 N
(d) 16 N

Answer: A

Question. The two waves of the same frequency moving in the same direction give rise to
(a) Interference
(b) Stationary waves
(c) None of these
(d) Beats

Answer: A

Question. The string of a violin emits a note of 205 Hz at its correct tension. The string is tightened slightly and then it produces six beats in two seconds with a tuning fork of frequency 205 Hz. The frequency of the note emitted by the taut string is
(a) 208 Hz
(b) 202 Hz
(c) 199 Hz
(d) 211 Hz

Answer: A

Question. When two tuning forks (fork 1 and fork 2) are sounded together, 4 beats per second are heard. Now some tape is attached on the prong of the fork 2. When the tuning forks are sounded again, 6 beats per second are heard. If the frequency of fork 1 is 200 Hz, then what was the original frequency of fork 2?
(a) 196 Hz
(b) 204 Hz
(c) 202 Hz
(d) 200 Hz

Answer: A

Question. A hospital uses an ultrasonic scanner to locate tumours in a tissue. The operating frequency of the scanner is 4.2 MHz. The speed of sound in a tissue is 1.7 km/s. The wavelength of sound in the tissue is close to
(a) 4 × 10^–4 m
(b) 4 × 10^–3 m
(c) 8 × 10^–3 m
(d) 8 × 10^–4 m

Answer: A

Question. Sound waves travel at 350 m/s through a warm air and at 3500 m/s through brass. The wavelength of a 700 Hz acoustic wave as it enters brass from warm air
(a) Increases by a factor 10
(b) Decreases by a factor 10
(c) Decreases by a factor 20
(d) Increases by a factor 20

Answer: A

Question. The driver of a car travelling with speed 30 m/s towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 m/s, the frequency of reflected sound as heard by driver is
(a) 720 Hz
(b) 555.5 Hz
(c) 550 Hz
(d) 500 Hz

Answer: A

Question. The intensity of sound reduces by 20% on passing through a glass slab. If sound of intensity I is made to cross through two such slabs, then the intensity of emergent sound will be
(a) 0.64 I
(b) 0.4 I
(c) 0.8 I
(d) 0.36 I

Answer: A

Question. A stationary wave is represented by y = A sin (100t) cos (0.01x), where y and A are in millimetres, t is in second and x is in metre. The velocity of the constituent wave is
(a) 10⁴ m/s
(b) Not derivable
(c) 1 m/s
(d) 10² m/s

Answer: A

Question. The length of a sonometer wire AB is 110 cm. Where should the two bridges be placed from A to divide the wire in 3 segments whose fundamental frequencies are in the ratio of 1 : 2 : 3?
(a) 60 cm and 90 cm
(b) 30 cm and 60 cm
(c) 30 cm and 90 cm
(d) 40 cm and 80 cm

Answer: A

Question. Standing waves are produced in 10 m long stretched string fixed at both ends. If the string vibrates in 5 segments and wave velocity is 20 m/s, the frequency is
(a) 5 Hz
(b) 10 Hz
(c) 2 Hz
(d) 4 Hz

Answer: A

Question. For a particular resonance tube, following are four of the six harmonics below 1000 Hz; 300, 600, 750 and 900 Hz .The two missing harmonics are
(a) 150, 450
(b) 400, 800
(c) 250, 400
(d) 75, 150

Answer: A

Question. In a standing wave, all particles of the medium cross the mean position with
(a) Different speeds at same instant
(b) Same speed at same instant
(c) Different speeds at different instants
(d) Same speed at different instants

Answer: A

Question. 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
(a) 9 : 4
(b) 4 : 9
(c) 2 : 3
(d) 3 : 2

Answer: A

Question. Two identical piano wires, kept under the same tension T have a fundamental frequency of 600 Hz. The fractional increase in the tension of one of the wires which will lead to occurrence of 6 beats per second when both the wires oscillate together would be
(a) 0.02
(b) 0.03
(c) 0.01
(d) 0.04

Answer: A

Question. A wave of frequency 100 Hz travels along a string towards its fixed end. When this wave travels back, after reflection, a node is formed at a distance of 10 cm from the fixed end. The speed of the wave (incident and reflected) is
(a) 20 m/s
(b) 40 m/s
(c) 5 m/s
(d) 10 m/s

Answer: A

Question. A standing wave having 3 nodes and 2 antinodes is formed between two atoms having a distance 1.21 Å between them. The wavelength of the standing wave is
(a) 1.21 Å
(b) 3.63 Å
(c) 2.42 Å
(d) 6.05 Å

Answer: A

Question. A wave in a string has an amplitude of 2 cm. The wave travels in the +ve direction of x axis with a speed of 128 m/s and it is noted that 5 complete waves fit in 4 m length of the string. The equation describing the wave is
(a) y = (0.02) m sin(7.85x – 1005t)
(b) y = (0.02) m sin(7.85x + 1005t)
(c) y = (0.02) m sin(15.7x + 2010t)
(d) y = (0.02) m sin(15.7x – 2010t)

Answer: A

Question. Two waves of wavelengths 50 cm and 51 cm produced 12 beats per second. The velocity of sound is
(a) 306 m/s
(b) 360 m/s
(c) 331 m/s
(d) 340 m/s

Answer: A

Question. Two sound waves with wavelengths 5.0 m and 5.5 m respectively, each propagate in a gas with velocity 330 m/s. We expect the following number of beats per second
(a) 6
(b) 12
(c) Zero
(d) 1

Answer: A

Question. Each of the two strings of length 51.6 cm and 49.1 cm are tensioned separately by 20 N force. Mass per unit length of both the strings is same and equal to 1 g/m. When both the strings vibrate simultaneously the number of beats is
(a) 7
(b) 8
(c) 5
(d) 3

Answer: A

Question. A tuning fork of frequency 512 Hz makes 4 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per second when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was
(a) 508 Hz
(b) 510 Hz
(c) 514 Hz
(d) 516 Hz

Answer: A

Question. Which one of the following statements is true?
(a) The sound waves in air are longitudinal while the light waves are transverse
(b) Both light and sound waves in air are longitudinal
(c) Both light and sound waves can travel in vacuum
(d) Both light and sound waves in air are transverse

Answer: A