Home / Aptitude Tests / Physics / A turning fork of fr...
A turning fork of frequency 340Hz is vibrated just above a c...

A turning fork of frequency 340Hz is vibrated just above a cylindrical tube of height 1.2m. If water is slowly poured into the tube, at what maximum height will resonance occur.
[speed of sound in air = 340ms-1]

A.

0.95m

B.

0.60m

C.

0.50m

D.

0.45m

Correct answer is D

In vibration in a closed pipe/tube, the first resonance occurs at a position L = V/4f,
when reading from the top of the tube,

L1 =_340
4 x 340

= 0.25m
L2 = 3V/4f
L2 = 3 x 340
4 x 340

= 0.75m
L3 = 5V/4f
L3 = 5 x 340
4 x 340

= 1.25m
However, the effective length of the tube is 1.2m. Thus reading from below, the first position of resonance will be 1.20 - 0.75m = 0.45m