passwella.
Menu

JAMB Physics 2001 Question 12

Question 12

Sound

Find the frequencies of the first three harmonics of a piano string of length 1.5 m, if the velocity of the waves on the string is 120 m s−1.

  1. A.40 Hz, 80 Hz, 120 Hz
  2. B.80 Hz, 160 Hz, 240 Hz
  3. C.180 Hz, 360 Hz, 540 Hz
  4. D.360 Hz, 180 Hz, 90 Hz
Show the answer and explanation

Answer: A (40 Hz, 80 Hz, 120 Hz)

Explanation

The fundamental has λ = 2L = 3 m, so f0 = 120/3 = 40 Hz. A string gives all multiples: 40 Hz, 80 Hz and 120 Hz.