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Oscillations — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsOscillations4 Marks
Question
Read the passage given below and answer the following questions from (i) to (v).
When a system (such as a simple pendulum or a block attached to a spring) is displaced from its equilibrium position and released, it oscillates with its natural frequency $\omega,$ and the oscillations are called free oscillations. All free oscillations eventually die out because of the ever present damping forces. However, an external agency can maintain these oscillations. These are called forced or driven oscillations. We consider the case when the external force is itself periodic, with a frequency wd called the driven frequency. The most important fact of forced periodic oscillations is that the system oscillates not with its natural frequency $\omega,$ but at the frequency $\omega,$ d of the external agency; the free oscillations die out due to damping. The most familiar example of forced oscillation is when a child in a garden swing periodically presses his feet against the ground (or someone else periodically gives the child a push) to maintain the oscillations. The maximum possible amplitude for a given driving frequency is governed by the driving frequency and the damping, and is never infinity. The phenomenon of increase in amplitude when the driving force is close to the natural frequency of the oscillator is called resonance. In our daily life, we encounter phenomena which involve resonance. Your experience with swings is a good example of resonance. You might have realized that the skill in swinging to greater heights lies in the synchronization of the rhythm of pushing against the ground with the natural frequency of the swing.
  1. When a system oscillates with its natural frequency ω, and the oscillations are called:
  1. Free oscillations.
  2. Forced oscillations.
  1. All free oscillations eventually die out because of:
  1. Damping force.
  2. electromagnetic force.
  3. None of these.
  1. What is free oscillation?
  2. What is forced oscillations?
  3. What is resonance?
✓

Answer

  1. a) Free oscillations.
  2. a) Damping force.
  3. When a system (such as a simple pendulum or a block attached to a spring) is displaced from its equilibrium position and released, it oscillates with its natural frequency ω, and the oscillations are called free oscillations.
  4. Forced oscillations are oscillations where external force drives the oscillations with frequency given by external force.
  5. The phenomenon of increase in amplitude when the driving force is close to the natural frequency of the oscillator is called resonance. In our daily life, we encounter phenomena which involve resonance. Your experience with swings is a good example of resonance. You might have realized that the skill in swinging to greater heights lies in the synchronization of the rhythm of pushing against the ground with the natural frequency of the swing.

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