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]
[speed of sound in air = 340ms-1]
-
A.
0.95m -
B.
0.60m -
C.
0.50m -
D.
0.45m
Correct Answer: Option D
Explanation
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