This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Longitudinal Waves”.
1. The displacement of a particle varies according to the relation
The amplitude of the particle is
2. The displacement y of a particle in a medium can be expressed as
Where t is in seconds and x in meter. The speed of the wave is
Explanation: y=10-6 sin(100t+20x+π/4)
Comparing with standard equation,
3. The displacement y of a wave travelling in the x direction is given by
Where x is expressed in meters and t is seconds. The speed of the wave motion (in m/s) is
Explanation: y=10-4 sin(600t-2x+π/3)
ω=600 rad s-1,k=2 rad/m
4. A wave y=asin(ωt-kx), on a string meets with another wave producing a node at x = 0. Then, the equation of the unknown wave is
Explanation: For producing node, the superposing wave must travel in the opposite direction (x term must have opposite sign) and its displacement must be negative. Hence the correct option is b
At x=0, y = 0. That is a node is formed.
5. The speed of sound in oxygen (O2) at a certain temperature is 460m/s. The speed of sound in helium (He) at the same temperature will be (assume both gases to be ideal)
Explanation: vHe/v(O2) =√(γHe/γ(O2) ×M(O2)/MHe)=√((5/3)/(7/5)×32/4)=√(200/21)
6. Length of a string tied to two rigid supports is 40cm. Maximum length (wavelength in cm) of a stationary wave produced on it is
Explanation: When the string vibrates in one segment,
7. A metal wire of linear mass density of 9.8/gm is stretched with a tension of 10kg wt between two rigid supports 1m apart. The wire passes at its middle point between the poles of a permanent magnet and it vibrates in resonance, when carrying an alternating current of frequency v. The frequency v of the alternating source is
a) 50 Hz
b) 100 Hz
c) 200 Hz
d) 25 Hz
Explanation: Here, m=9.8/gm=9.8×10-3 kg/m
T=10kg wt = 9.8×10=98N
The fundamental frequency of vibration of the string,
8. A sound absorber attenuates the sound level by 20dB. The intensity decreases by a factor of
Explanation: L1=10log(I1/I0) L2=10log(I2/I0)
I1/I2 =102 I2=1/100×I1.
9. The ratio of velocity of sound in hydrogen and oxygen at STP is
Explanation: vH/vO =√(MO/MH)=√(32/2)=4:1.
10. It takes 2 seconds for a second wave to travel between two fixed points when the day temperature is 10°C. If the temperature rises to 30°C, the sound wave travels between the same fixed parts in
a) 1.9 sec
b) 2 sec
c) 2.1 sec
d) 2.2 sec
Explanation: v∝1/√T and t∝1/v
Sanfoundry Global Education & Learning Series – Engineering Physics.
To practice all areas of Engineering Physics, here is complete set of 1000+ Multiple Choice Questions and Answers.