# Competitive Exams: Physics MCQs (Practice_Test 20 of 35)

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- Two tuning forks A and B produce notes of frequencies 256 Hz and 262 Hz respectively. An unknown note sounded at the same time as a produces beats, When the same note is sounded with B, be at frequency is twice as large. Two unknown frequency could be
- 268 Hz
- 260 Hz
- 250 Hz
- 242 Hz

- A sound wave of frequency f propagating through air with a velocity C, is reflected from a surface which is moving away from the source with a constant speed v. The frequency of1he reflected wave, measured by the observer at the position of the source, is
- f (C-v) /C + v
- f (C + v) /C-v
- f (C + 2v) /C + v
- f (C + v) /C − 2v

- A wire is stretched by one mm by a force of 1 kN. The work done in stretching the wire is
- 5 ergs
- 5 Joules
- 0.5 ergs
- 0.5 Joules

- A damped source of sound is set into vibration by an external force with a frequency W. When W is much larger than the natural frequency of the source, the average energy stored in the source is
- mostly in the form of heat energy
- mostly 1n the form of potential energy
- mostly in the form of kinetic energy.
- equally divide among kinetic and potential energies

- A string of length 2 m is fixed at both ends; If this string vibrates in its fourth normal mode with a frequency of 500 Hz, then the waves would travel on it with a velocity of
- 125 m/s
- 250 m/s
- 500 m/s
- 1000 m/s

- A one metre long string of mass 4.9 × 10 − 4 kg is held under a tension of 19.6 Newtons. If the string vibrates in one segment, then the frequency of vibration will be
- 200 Hz
- 100Hz
- 50 Hz
- 400 Hz

- Consider the following statements about ultrasonic waves:
- Ultrasonic waves travel faster than ordinary sound waves.
- Bats can produce ultrasonic waves.
- Quartz crystal used to produce ultrasonic waves.
- Ultrasonic waves are used in quartz watches.

Of these statements

- 1,2 and 4 are correct
- 1 and 3 are correct
- 2 and 3 are correct
- 1,2, 3 and 4 are correct

- A piezoelectric X-cut quartz plate has a thickness of 1.5 mm. If the velocity of propagation of longitudinal sound waves along the X-direction is 5700 m/s, then the fundamental frequency of crystal will be.
- 1.5 MHz
- 1.9MHz
- 3.8 MHz
- 8.6 MHz

- The power (in dioptres) of an equiconvex lens with radii of curvature of10cm and refractive index of 1.6 is
- -12
- + 12
- + 1.2
- -1.2

- A convex lens of focal length 10 cm forms the image at the least distance of distinct vision. The magnification produced is
- 1.5
- 3.5
- 4.5
- 5.5

- If two + 5 dioptre lenses are mounted at some distance apart, the equivalent power will always be negative if the distance is:
- greater than 40 cm
- equal to 40cm
- equal to 10 cm
- less than10cm

- A Galileo telescope has an objective of focal length. 100 cm and magnifying power 50. The distance between the two lenses in-normal adjustment will be
- 98 cm
- 100 cm
- 150 cm
- 200

- A light source of candle power is placed at a distance of 30 cm from the grease spot of a photometer. For the disappearance of grease spot, a source of 16 candle power should be placed on the other side of the grease spot, at a distance of
- 17.0cm
- 40.0cm
- 53.0cm
- 95.0 cm

- When a light wave travels from one medium to another, the characteristic parameter that remains invariant is
- wave length
- velocity
- frequency
- intensity

- In a Young double slit experiment the aperture screen distance is 2 m. The fringe width is 1 mm. Light of 600 mm is used if a thin plate of glass (m = 1.5) of thickness 0.06mm is placed over one of the slits, then there will be a lateral displacement of the fringes by
- 0 cm
- 5 cm
- 10 cm
- 15 cm