Class 11 Physics Chapter 13 Oscillations – Revision Notes

Oscillatory motion in this chapter starts from the defining SHM condition a=−ω²x and the standard displacement, velocity, and acceleration equations that follow from it. It then covers how kinetic and potential energy interconvert while total mechanical energy stays constant, and how pendulum and spring-mass periods are calculated.

Last Updated: September 23, 2026

SHM Basics

• Condition: a=−ω²x.
• x=A sin(ωt+φ); v=Aωcos(ωt+φ); a=−Aω²sin(ωt+φ).

Energy

• E=½mω²A² (constant); KE and PE interconvert.

Time Periods

• Simple pendulum: T=2π√(l/g).
• Spring-mass: T=2π√(m/k).

One-Line Summary

Oscillations describe periodic to-and-fro motion, with simple harmonic motion being the special case where restoring force is proportional to displacement, conserving total mechanical energy throughout.

Quick visual: a worked diagram from the full Solutions page, for reference.

Frequently Asked Questions

What makes a motion simple harmonic rather than just periodic?
A periodic motion is simple harmonic only if the restoring force is directly proportional to the displacement from the mean position and always directed toward that mean position, producing the characteristic sinusoidal variation with time.

How is the time period of a simple pendulum related to its length?
The time period of a simple pendulum is directly proportional to the square root of its length, meaning a longer pendulum takes more time to complete one oscillation, while the period is independent of the mass of the bob.

Written by Satish

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