# AFCAT: Physics MCQs (Practice-Test 20 of 35)

1. 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

1. 268 Hz

2. 260 Hz

3. 250 Hz

4. 242 Hz

2. 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

1. f (C-v)/C + v

2. f (C + v)/C-v

3. f (C + 2v)/C + v

4. f (C + v)/C − 2v

3. A wire is stretched by one mm by a force of 1 kN. The work done in stretching the wire is

1. 5 ergs

2. 5 Joules

3. 0.5 ergs

4. 0.5 Joules

4. 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

1. mostly in the form of heat energy

2. mostly 1n the form of potential energy

3. mostly in the form of kinetic energy.

4. equally divide among kinetic and potential energies

5. 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

1. 125 m/s

2. 250 m/s

3. 500 m/s

4. 1000 m/s

6. 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

1. 200 Hz

2. 100Hz

3. 50 Hz

4. 400 Hz

7. Consider the following statements about ultrasonic waves:

1. Ultrasonic waves travel faster than ordinary sound waves.

2. Bats can produce ultrasonic waves.

3. Quartz crystal used to produce ultrasonic waves.

4. Ultrasonic waves are used in quartz watches.

Of these statements

1. 1, 2 and 4 are correct

2. 1 and 3 are correct

3. 2 and 3 are correct

4. 1, 2, 3 and 4 are correct

8. 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. 1.5 MHz

2. 1.9MHz

3. 3.8 MHz

4. 8.6 MHz

9. The power (in dioptres) of an equiconvex lens with radii of curvature of10cm and refractive index of 1.6 is

1. -12

2. + 12

3. + 1.2

4. -1.2

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

1. 1.5

2. 3.5

3. 4.5

4. 5.5

11. If two + 5 dioptre lenses are mounted at some distance apart, the equivalent power will always be negative if the distance is:

1. greater than 40 cm

2. equal to 40cm

3. equal to 10 cm

4. less than10cm

12. 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

1. 98 cm

2. 100 cm

3. 150 cm

4. 200

13. 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

1. 17.0cm

2. 40.0cm

3. 53.0cm

4. 95.0 cm

14. When a light wave travels from one medium to another, the characteristic parameter that remains invariant is

1. wave length

2. velocity

3. frequency

4. intensity

15. 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

1. 0 cm

2. 5 cm

3. 10 cm

4. 15 cm

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