Waves

35 free MDCAT Physics MCQs on Waves (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

Tap an answer to check it · 35 questions

1. Question 1

   The to and fro motion of a body about its mean position is called:
   • AVibratory motion
   • BRotational motion
   • CTranslational motion
   • DRandom motion
   Show answer and explanation

   Answer: A) Vibratory motion

   e.g. a swinging pendulum. Source: PHYSICS 11 KPK (taleem360.com), p. 226.

2. Question 2

   The time required by a vibrating body to complete one vibration is its:
   • AFrequency
   • BTime period
   • CAmplitude
   • DWavelength
   Show answer and explanation

   Answer: B) Time period

   T = 1/f. Source: PHYSICS 11 KPK (taleem360.com), p. 226.

3. Question 3

   The number of vibrations completed by a body in one second is its:
   • AAmplitude
   • BTime period
   • CFrequency
   • DAngular velocity
   Show answer and explanation

   Answer: C) Frequency

   Unit hertz (Hz). Source: PHYSICS 11 KPK (taleem360.com), p. 226.

4. Question 4

   The maximum displacement of a vibrating body from its mean position is its:
   • APeriod
   • BWavelength
   • CDisplacement
   • DAmplitude
   Show answer and explanation

   Answer: D) Amplitude

   Displacement is the distance at any instant. Source: PHYSICS 11 KPK (taleem360.com), p. 227.

5. Question 5

   Motion in which acceleration is directly proportional to displacement from the mean position and always directed towards it is:
   • ASimple harmonic motion
   • BUniform circular motion
   • CProjectile motion
   • DUniform linear motion
   Show answer and explanation

   Answer: A) Simple harmonic motion

   a = -(k/m) x for a mass on a spring. Source: PHYSICS 11 KPK (taleem360.com), p. 228.

6. Question 6

   Waves having a constant phase difference and the same frequency are called:
   • APolarized waves
   • BCoherent waves
   • CStationary waves
   • DLongitudinal waves
   Show answer and explanation

   Answer: B) Coherent waves

   Coherence is needed for a steady interference pattern; a laser is a coherent source. Source: 11 Physics Book FBISE, p. 162.

7. Question 7

   For each 1 C rise in temperature, the speed of sound in air increases by about:
   • A1.61 m/s
   • B0.61 m/s
   • C6.1 m/s
   • D0.16 m/s
   Show answer and explanation

   Answer: B) 0.61 m/s

   v = v0 + 0.61 t. Source: PHYSICS 11 KPK (taleem360.com), p. 265.

8. Question 8

   Steel has density 7800 kg/m3 and elastic modulus 2.0 x 10^11 N/m2. The speed of sound in it is about:
   • A1.43 x 10^3 m/s
   • B332 m/s
   • C5.06 x 10^3 m/s
   • D2.56 x 10^7 m/s
   Show answer and explanation

   Answer: C) 5.06 x 10^3 m/s

   v = sqrt(E/rho) = sqrt(2.0e11/7800) = 5.06 x 10^3 m/s. Source: PHYSICS 11 KPK (taleem360.com), p. 265.

9. Question 9

   Beats cannot be heard as separate if their number per second is more than:
   • A100
   • B2
   • C50
   • D10
   Show answer and explanation

   Answer: D) 10

   The ear cannot separate faster fluctuations. Source: 11 Physics Book FBISE, p. 165.

10. Question 10

    Edwin Hubble's observation that all galaxies are red-shifted, suggesting the universe is expanding, was made in:
    • A1842
    • B1929
    • C1965
    • D1800
    Show answer and explanation

    Answer: B) 1929

    Red shift means the source is moving away. Source: 11 Physics Book FBISE, p. 160.

11. Question 11

    When unpolarized light passes through a Polaroid filter, its intensity becomes:
    • AUnchanged
    • BOne fourth
    • CZero
    • DHalf
    Show answer and explanation

    Answer: D) Half

    Only one plane of vibration is transmitted. Source: 11 Physics Book FBISE, p. 175.

12. Question 12

    Unpolarized light of 16 W/m2 passes two polarizers whose axes differ by 30. The transmitted intensity is:
    • A16 W/m2
    • B8 W/m2
    • C6 W/m2
    • D2 W/m2
    Show answer and explanation

    Answer: C) 6 W/m2

    First polarizer: 8 W/m2; then 8 cos^2 30 = 6 W/m2 (Malus's law). Source: 11 Physics Book FBISE, p. 177.

13. Question 13

    A guitar string 80.0 cm long carries waves at 400 m/s. The frequency of its third harmonic is:
    • A1000 Hz
    • B250 Hz
    • C500 Hz
    • D750 Hz
    Show answer and explanation

    Answer: D) 750 Hz

    f1 = v/2L = 250 Hz; f3 = 3 f1 = 750 Hz. Source: 11 Physics Book FBISE, p. 175.

14. Question 14

    A 0.5 kg mass hung from a spring stretches it by 0.098 m. The spring constant is:
    • A50 N/m
    • B4.9 N/m
    • C0.098 N/m
    • D490 N/m
    Show answer and explanation

    Answer: A) 50 N/m

    k = mg/x = 4.9/0.098 = 50 N/m. Source: PHYSICS 11 KPK (taleem360.com), p. 229.

15. Question 15

    Tuning forks of 440 Hz and 437 Hz are sounded together. The number of beats heard in 10 s is:
    • A300
    • B3
    • C877
    • D30
    Show answer and explanation

    Answer: D) 30

    Beat frequency 3 Hz x 10 s = 30 beats. Source: 11 Physics Book FBISE, p. 183.

16. Question 16

    A 1.2 m string vibrates in its third harmonic. The wavelength is:
    • A0.8 m
    • B2.4 m
    • C1.2 m
    • D3.6 m
    Show answer and explanation

    Answer: A) 0.8 m

    Wavelength = 2L/n = 2.4/3 = 0.8 m. Source: 11 Physics Book FBISE, p. 183.

17. Question 17

    A train's 150 Hz horn approaches a stationary person at 35.0 m/s (speed of sound 340 m/s). The person hears about:
    • A136 Hz
    • B167 Hz
    • C150 Hz
    • D185 Hz
    Show answer and explanation

    Answer: B) 167 Hz

    f' = f v/(v - vs) = 150 x 340/305 = 167 Hz; 136 Hz after it passes. Source: 11 Physics Book FBISE, p. 183.

18. Question 18

    Polarized light of intensity I0 passes a polarizer whose axis is at 60 to its plane of polarization. The transmitted intensity is:
    • A0.75 I0
    • B0.5 I0
    • C0.25 I0
    • D0.87 I0
    Show answer and explanation

    Answer: C) 0.25 I0

    Malus's law: I = I0 cos^2 60 = I0/4. Source: 11 Physics Book FBISE, p. 183.

19. Question 19

    The time period of a simple pendulum does not depend on the:
    • AValue of g
    • BLength of the pendulum
    • CMass of the bob
    • DPlace on the Earth
    Show answer and explanation

    Answer: C) Mass of the bob

    T = 2 pi sqrt(l/g). Source: PHYSICS 11 KPK (taleem360.com), p. 233.

20. Question 20

    If the length of a simple pendulum is increased, its time period:
    • ABecomes zero
    • BBecomes smaller
    • CStays the same
    • DBecomes greater
    Show answer and explanation

    Answer: D) Becomes greater

    T is proportional to sqrt(l). Source: PHYSICS 11 KPK (taleem360.com), p. 233.

21. Question 21

    Troops are told not to march in step across a suspension bridge to avoid:
    • AResonance
    • BDamping
    • CBeats
    • DDiffraction
    Show answer and explanation

    Answer: A) Resonance

    Periodic impulses matching the bridge's natural period could build dangerous amplitudes. Source: PHYSICS 11 KPK (taleem360.com), p. 237.

22. Question 22

    Tuning a radio to a station is an example of:
    • AMechanical damping
    • BElectrical resonance
    • CSound interference
    • DLight polarization
    Show answer and explanation

    Answer: B) Electrical resonance

    The circuit's natural frequency is matched to the station's frequency. Source: PHYSICS 11 KPK (taleem360.com), p. 237.

23. Question 23

    A microwave oven heats food because the microwave frequency matches the natural frequency of:
    • AGlass molecules
    • BMetal atoms
    • CWater molecules
    • DAir molecules
    Show answer and explanation

    Answer: C) Water molecules

    The water molecules resonate and absorb energy. Source: PHYSICS 11 KPK (taleem360.com), p. 238.

24. Question 24

    When a wave travels along a cord:
    • AOnly the disturbance moves
    • BThe particles move with it
    • CThe cord moves as a whole
    • DNo energy is carried
    Show answer and explanation

    Answer: A) Only the disturbance moves

    Particles only oscillate about their mean positions; energy is transferred. Source: PHYSICS 11 KPK (taleem360.com), p. 253.

25. Question 25

    A necessary condition for mechanical waves to propagate is that the medium must be:
    • ARigid
    • BElastic
    • CTransparent
    • DConducting
    Show answer and explanation

    Answer: B) Elastic

    Particles must also exert forces on one another. Source: PHYSICS 11 KPK (taleem360.com), p. 253.

26. Question 26

    Sound travels faster in damp air than in dry air because moisture:
    • ARaises the air temperature
    • BIncreases the air pressure
    • CReduces the air's density
    • DMakes the air more rigid
    Show answer and explanation

    Answer: C) Reduces the air's density

    v is inversely proportional to the square root of density. Source: PHYSICS 11 KPK (taleem360.com), p. 263.

27. Question 27

    Light from a star moving away from the Earth shows a:
    • ABlue shift
    • BRed shift
    • CNo shift
    • DPolarization
    Show answer and explanation

    Answer: B) Red shift

    Frequencies shift lower; a blue shift means approach. Source: 11 Physics Book FBISE, p. 160.

28. Question 28

    Radar speed traps measure the speed of vehicles by using the:
    • APolarization effect
    • BInterference effect
    • CDoppler effect
    • DMagnus effect
    Show answer and explanation

    Answer: C) Doppler effect

    The reflected radio wave's frequency changes with the vehicle's motion. Source: 11 Physics Book FBISE, p. 160.

29. Question 29

    Constructive interference occurs when:
    • AWaves travel opposite ways
    • BCrest falls on trough
    • CWaves have unequal frequency
    • DCrest falls on crest
    Show answer and explanation

    Answer: D) Crest falls on crest

    The resultant amplitude is the sum of the amplitudes. Source: 11 Physics Book FBISE, p. 162.

30. Question 30

    Noise-cancelling headphones produce a wave of equal amplitude and:
    • AOpposite phase
    • BDouble frequency
    • CSame phase
    • DHalf wavelength
    Show answer and explanation

    Answer: A) Opposite phase

    The 180 out-of-phase wave interferes destructively with the noise. Source: 11 Physics Book FBISE, p. 164.

31. Question 31

    In a stationary wave, energy is:
    • ATransferred at wave speed
    • BNot transferred along it
    • CTransferred only at nodes
    • DDestroyed at antinodes
    Show answer and explanation

    Answer: B) Not transferred along it

    It is confined between nodes and antinodes. Source: 11 Physics Book FBISE, p. 167.

32. Question 32

    A closed organ pipe (closed at one end) produces:
    • AOnly even harmonics
    • BAll harmonics
    • COnly odd harmonics
    • DNo harmonics
    Show answer and explanation

    Answer: C) Only odd harmonics

    Fundamental v/4L; an open pipe has fundamental v/2L and all harmonics. Source: 11 Physics Book FBISE, p. 174.

33. Question 33

    Polarization is a phenomenon shown only by:
    • AStationary waves
    • BLongitudinal waves
    • CSound waves
    • DTransverse waves
    Show answer and explanation

    Answer: D) Transverse waves

    It shows that light is a transverse wave. Source: 11 Physics Book FBISE, p. 175.

34. Question 34

    Diffraction is clearly observed when the size of the gap or obstacle is:
    • AComparable to the wavelength
    • BMuch larger than wavelength
    • CExactly zero
    • DLarger than the source
    Show answer and explanation

    Answer: A) Comparable to the wavelength

    For larger obstacles only slight bending occurs at the edges. Source: 11 Physics Book FBISE, p. 178.

35. Question 35

    Gravitational waves were detected using:
    • APolaroid filters
    • BLaser interferometers
    • COrgan pipes
    • DRadar sets
    Show answer and explanation

    Answer: B) Laser interferometers

    LIGO arms change length by a tiny fraction of a proton's width. Source: 11 Physics Book FBISE, p. 180.

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