Waves, Sound, Pendulum and Simple Harmonic Motion

Attempt the quiz above first, then review every question with its correct answer and a short explanation below.

1. Q1.Sound cannot travel through:

   • A.air
   • B.water
   • C.steel
   • D.a vacuum✓ Correct Answer

   Explanation: Sound needs a material medium.

2. Q2.The SI unit of frequency is:

   • A.decibel
   • B.hertz✓ Correct Answer
   • C.metre
   • D.watt

   Explanation: One hertz is one cycle per second.

3. Q3.Sound waves in air are:

   • A.transverse
   • B.electromagnetic
   • C.longitudinal✓ Correct Answer
   • D.stationary only

   Explanation: Particles vibrate along the direction of travel.

4. Q4.An echo is produced by the:

   • A.reflection of sound✓ Correct Answer
   • B.refraction of sound
   • C.absorption of sound
   • D.diffraction of light

   Explanation: Sound bounces off a distant surface.

5. Q5.Light waves are:

   • A.longitudinal mechanical waves
   • B.transverse electromagnetic waves✓ Correct Answer
   • C.sound waves
   • D.stationary waves

   Explanation: They need no medium to travel.

6. Q6.The pitch of a sound depends on its:

   • A.amplitude
   • B.speed
   • C.frequency✓ Correct Answer
   • D.loudness only

   Explanation: Higher frequency gives a shriller sound.

7. Q7.The speed of sound in air at ordinary temperature is about:

   • A.34 m/s
   • B.3,400 m/s
   • C.340 m/s✓ Correct Answer
   • D.3 × 10^8 m/s

   Explanation: It increases with temperature.

8. Q8.Sound travels fastest in:

   • A.solids✓ Correct Answer
   • B.gases
   • C.liquids
   • D.a vacuum

   Explanation: Closely packed particles pass vibrations quickly.

9. Q9.The audible range of frequencies for humans is about:

   • A.2 Hz to 200 Hz
   • B.200 Hz to 2 kHz
   • C.20,000 Hz to 2 lakh Hz
   • D.20 Hz to 20,000 Hz✓ Correct Answer

   Explanation: Below 20 Hz is infrasonic and above 20,000 Hz is ultrasonic.

10. Q10.Sound waves with frequency above 20,000 Hz are called:

    • A.infrasonic waves
    • B.radio waves
    • C.ultrasonic waves✓ Correct Answer
    • D.audible waves

    Explanation: Bats and dolphins use ultrasound.

11. Q11.The loudness of sound is measured in:

    • A.decibel✓ Correct Answer
    • B.hertz
    • C.watt
    • D.pascal

    Explanation: The decibel scale is logarithmic.

12. Q12.The relation among wave speed v, frequency f and wavelength λ is:

    • A.v = fλ✓ Correct Answer
    • B.v = f/λ
    • C.v = λ/f²
    • D.v = f + λ

    Explanation: Speed equals frequency times wavelength.

13. Q13.The time period of a simple pendulum depends on:

    • A.the mass of the bob
    • B.the material of the bob
    • C.its length and g✓ Correct Answer
    • D.the amplitude only

    Explanation: T = 2π√(L/g) for small oscillations.

14. Q14.The minimum distance of a reflecting surface needed to hear a distinct echo is about:

    • A.1.7 m
    • B.17 m✓ Correct Answer
    • C.170 m
    • D.340 m

    Explanation: Sound needs 0.1 s to go and return, covering about 34 m.

15. Q15.The Doppler effect is the apparent change in:

    • A.speed of light in a medium
    • B.mass of a body
    • C.temperature of a gas
    • D.frequency due to relative motion of source and observer✓ Correct Answer

    Explanation: A passing siren sounds higher while approaching and lower while receding.

16. Q16.Resonance occurs when:

    • A.the amplitude is zero
    • B.the medium is a vacuum
    • C.the mass is doubled
    • D.the driving frequency equals the natural frequency✓ Correct Answer

    Explanation: The amplitude then becomes large.

17. Q17.SONAR makes use of:

    • A.radio waves
    • B.ultrasonic waves✓ Correct Answer
    • C.X-rays
    • D.infrared radiation

    Explanation: It finds underwater objects from reflected sound pulses.

18. Q18.In simple harmonic motion, the acceleration is:

    • A.proportional to displacement and directed towards the mean position✓ Correct Answer
    • B.constant in magnitude
    • C.zero at the extremes
    • D.proportional to velocity

    Explanation: a = -ω²x.

19. Q19.If the length of a simple pendulum is made four times, its time period becomes:

    • A.four times
    • B.twice✓ Correct Answer
    • C.half
    • D.one-fourth

    Explanation: T is proportional to √L.

20. Q20.The quality (timbre) of a musical note depends on its:

    • A.frequency alone
    • B.amplitude alone
    • C.speed alone
    • D.waveform (overtones present)✓ Correct Answer

    Explanation: It lets us tell a violin from a flute playing the same note.