In figure given below, A, B, C and D represent the test tubes each of height 20 cm which are filled with water up to heights of 12 cm, 14 cm, 16 cm and 18 cm respectively. If a vibrating tuning fork is placed over the mouth of test tube D, a loud sound is heard.

(a) Describe the observations with the tubes A, B and C when the vibrating tuning fork is placed over the mouth of these tubes.

(b) Give the reason for your observation in each tube.

(c) State the principle illustrated by the above experiment.

The unit of intensity of a sound wave is :

1. Wm
2. Wm^-2
3. Wm^-1
4. Wm^-3

For normal ears, sensitivity is maximum at the frequency :

1. 5 kHz
2. 10 kHz
3. 1 kHz
4. 500 Hz

By reducing the amplitude of the sound wave, its :

1. pitch decreases
2. loudness decreases
3. loudness increases
4. pitch increases