Unit-7 Oscillation Class 11 Physics | Important Short & Long Questions with Answers

Short and Long Questions with brief, board-standard answers for Unit-7 Oscillation (Class 11 Physics).

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SHORT QUESTIONS WITH BRIEF ANSWERS (Unit-7 Oscillation)

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Q1. What is oscillatory motion?

Ans: Motion in which a body moves repeatedly to and fro about a mean position is called oscillatory motion.

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Q2. Define simple harmonic motion (SHM).

Ans: SHM is a periodic motion in which the restoring force is directly proportional to displacement and always directed towards the mean position.

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Q3. Give two examples of free oscillations.

Ans:

1. Mass attached to a spring in vacuum

2. Simple pendulum in absence of air resistance

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Q4. What are forced oscillations?

Ans: Oscillations produced under the action of an external periodic force are called forced oscillations.

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Q5. Define amplitude.

Ans: Maximum displacement of a particle from its mean position is called amplitude.

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Q6. Define time period.

Ans: Time taken to complete one oscillation is called time period (T).

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Q7. Define frequency.

Ans: Number of oscillations per second is called frequency (f).

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Q8. What is angular frequency?

Ans: Rate of change of phase with time; $\omega =2\pi \mathrm{f.}$

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Q9. What is phase difference?

Ans: Difference in phase between two oscillating particles at the same instant.

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Q10. State the defining equation of SHM.

Ans:

$$a=-{\mathrm{\omega ²}}^{}x$$

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Q11. What happens to period if amplitude is doubled?

Ans: Time period remains unchanged because it is independent of amplitude.

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Q12. What is resonance?

Ans: When frequency of external force equals natural frequency, amplitude becomes maximum; this phenomenon is called resonance.

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Q13. Give two applications of resonance.

Ans:

1. Tuning of radio/TV circuits

2. Musical instruments

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Q14. What are damped oscillations?

Ans: Oscillations in which amplitude decreases with time due to friction or resistive forces.

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Q15. Why is acceleration zero at mean position in SHM?

Ans: Because displacement is zero, hence restoring force and acceleration are zero.

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Q16. Write formula of time period of spring-mass system.

Ans:

$$$$T=2πmkT = 2\pi \sqrt{\frac{m}{k}}

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Q17. Write formula of time period of simple pendulum.

Ans:

$$$$T=2πLgT = 2\pi \sqrt{\frac{L}{g}}

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Q18. What is critical damping?

Ans: Damping that brings a system to rest in minimum time without oscillation is called critical damping.

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Q19. What is energy exchange in SHM?

Ans: Kinetic and potential energies continuously interchange during SHM while total energy remains constant.

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Q20. What is frequency response curve?

Ans: Graph showing variation of amplitude with frequency of driving force.

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LONG / COMPREHENSIVE QUESTIONS WITH BRIEF EXAM ANSWERS

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Q1. Show that motion of a mass attached to a spring executes SHM.

Answer:
When a mass attached to a spring is displaced by x, restoring force is:

$$F = -kx$$

By Newton’s second law:

$$ma = -kx \Rightarrow a = -\frac{k}{m}x$$

Since acceleration is proportional to displacement and opposite in direction, the motion is SHM.

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Q2. Prove that projection of uniform circular motion on a diameter is SHM.

Answer:
For a particle moving in a circle, displacement along diameter is:

$$x = A \cos \omega t$$

Differentiating twice gives:

$$a = -\omega^2 x$$

Thus, projection of circular motion is SHM.

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Q3. Show that energy is conserved in SHM.

Answer:
Total energy:

$$E = KE + PE = \frac{1}{2} m \omega^2 A^2 = \text{constant}$$

As particle moves, KE converts into PE and vice versa, but total energy remains constant.

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Q4. Differentiate free and forced oscillations. Also define resonance.

Free Oscillations: Occur without external force; frequency is natural frequency.
Forced Oscillations: Occur under external periodic force; frequency equals driving force frequency.
Resonance: Maximum amplitude occurs when driving frequency equals natural frequency.

Applications:

1. Radio tuning

2. Musical instruments

3. Seismographs

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Q5. Derive equations for kinetic and potential energy in SHM.

Answer:
Potential Energy:

$$PE = \frac{1}{2} k x^2$$

Kinetic Energy:

$$KE = \frac{1}{2} m \omega^2 (A^2 - x^2)$$

Total Energy:

$$E = \frac{1}{2} k A^2$$

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Q6. Explain damped oscillations and importance of critical damping.

Answer:
Damped oscillations occur due to friction or resistance causing amplitude to decrease with time.
Critical damping is used in car suspension systems to stop vibrations quickly without oscillation, providing comfort and safety.

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Click on the link below for complete Class 11 Physics notes, MCQs, Q&A, and Numericals.

Class 11 Physics – Unit-wise MCQs & Study Resources (Main-Page)

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