# Units & Dimension and Wave & Acoustic

Q. Three basic concepts sufficient to describe quantitatively all the phenomena encountered in mechanical science are-

Ans. length mass and time

Q. In MKS system fourth unit besides meter kg and second as fundamental mechanical units are-

Ans. permeability of media

Q. For defining standard meter wavelength to which material is considered?

Ans. Krypton

Q. The number of basic SI units-

Ans. 7

Q. Supplementary units added to the basic SI units are-

Ans. 2

Q. Farad is the unit of-

Ans. Capacitance

Q. The dimension of force in SI system is-

Ans. LMT2

Applied Physics – Light

Q. During earthquake which waves are longitudinal in character?

Ans. P waves

Q. During earthquake the waves arriving at seismograph are-

Ans. P following by S

Q. A whistling engine is approaching a stationary observes with a velocity of 40 m/s. The velocity of sound in 330 m/s. The ratio of frequencies as heart by the observes at the time of approaching and passing of train is-

Ans. 2:1

Q. Human ears cannot detect the sounds of wavelength-

Ans. 100m

Q. The apparent frequency of the whistle of an engine changes in the ratio 6:5 as the engine passes a stationary observes. The velocity of engine in terms of sound c is-

Ans. C

Q. A passenger is sitting in a fast-moving train. The train blows a whistle of frequency N. If apparent frequency of sound is N’, then-

Ans. N’=N

Q. At what speed a source must move towards a stationary observer so that the apparent frequency may be double the true frequency of the source (c is velocity of the sound)-

Ans. c/2

Q. To a stationary man the frequency of sound source moving towards the man appears to be-

Ans. Higher than the original frequency

Q. In case wavelength of light coming from a star shifts towards the violet end of the spectrum, it can be concluded that the star is-

Ans. Approaching the earth

Q. Which of the following represents an elastic wave?

Ans. Microwaves

Q. At 27deg c longitudinal wave in which medium Will have the maximum velocity?

Ans. Air

Q. Doppler shift in frequency does not depend on-

Ans. The distance between source and the observes

Q. Which of the following frequency may not be detected by the human ear?

Ans. 10Hz

Q. The velocity of sound will be at least in

Ans. Distilled water

Q. When a body travels with a velocity greater than the velocity of sound than the shape of the wave front will be

Ans. Conical

Q. A source of the sound and an observer are moving away from other the apparent pitch will-

Ans. Decrease

Q. Smallest wavelength is of

Ans. infrasonic

Q. Change of atmospheric temperature affects which of the following property of sound?

Ans. Wavelength

Q. Beats are the result of-

Ans. Constructive and destructive interference

Q. A person while moving towards a mountain at a speed of 4 m/s hears a sound of frequency 510 Hz located behind him and its echo after reflection from the mountain the best frequency of the two sounds is

Ans. 12

Q. The velocity of sound waves will be at least while traveling through

Ans. Vacuum

Q. Formation of beats

Ans. Interference of waves

Q. In a ripple tank, two coherent sources are 12 cm apart at a distance 2 m away from the sources the maxima are 12.5 cm apart if the velocity of ripple is 30 cm/s in the tank then the frequency of the source is

Ans. 40Hz

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