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Question
Explain free and forced vibrations. Give an experimental arrangement to illustrate the phenomenon of resonance.
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Solution
When a system or a body vibrates without receiving impulses from another system or body, its vibrations are said to be free vibrations. However, when a system or body vibrates on account of impulses received from another system or body, the vibrations are called forced vibrations. In such a case the body or the system vibrates with the frequency of the impulses received and not with its natural frequency.
Experiment Arrangement to illustrate Resonance: In the figure, the two pendulums have exactly equal lengths. However, the bob of the pendulum A is heavier. Displace the bob of the pendulum A by a little distance in a direction perpendicular to the plane containing the two pendulums. Then release the bob. The pendulum A will begin to oscillate. After a short while, you will find that the pendulum B also begins to vibrate. Note that the two pendulums have the same frequency. The pendulum A through the rubber tube applies impulses of the same frequency on the pendulum B Hence, the pendulum B begins to vibrate.
RELATED QUESTIONS
Resonance is a special case of ______ vibrations, when frequency of the driving force is ______ natural frequency of the body.
A vibrating tuning fork, held over an air column of a given length with its one end closed, produces a loud audible sound. Name the phenomenon responsible for it and explain the observation.
When a body vibrates under a periodic force, the vibrations of the body are ______.
A tuning fork of frequency 256 Hz will resonate with another tuning fork of frequency:
In Fig. A, B, C and D are four pendulums suspended from the same elastic string XY. The lengths of pendulum A and D are equal, while the length of pendulum B is shorter and of the pendulum C is longer. Pendulum A is set into vibrations.
- What is your observation about the vibrations of pendulum D?
- Give reason for your observation in part (a).
- What type of vibrations take place in pendulums Band C?
- Give reason for the answer in part (c).
When acoustic resonance takes place, a loud sound is heard. Why does this happen? Explain.
Explain why stringed musical instruments, like the guitar, are provided with a hollow box.
