Physics
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.
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Answer
(a) No loud sound is heard with the tubes A and C, but a loud sound is heard with the tube B.
(b) Frequency of air column in tube D is equal to the frequency of tuning fork. Resonance occurs with the air column in tube B whereas no resonance occurs with the air column of tubes A and C. The frequency of vibrations of the air column in tube B is same as the frequency of vibrations of the air column in tube D because the length of the air column in tube D is 20 – 18 = 2 cm and that in tube B is 20 – 14 = 6 cm (i.e., three time). On the other hand, the frequency of vibrations of the air column in tubes A and C is not equal to the frequency vibrations of air column in tube D.
(c) When the frequency of vibrations of the air column is equal to the frequency of the vibrating tuning fork, resonance occurs.
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