Physics · Oscillations and waves · chapter 13 of 14

Class 11 Physics Chapter 13: Oscillations Assertion-reason questions with answers

2 assertion-reason questions on Oscillations, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): The acceleration of a particle in simple harmonic motion is zero at the instant it passes through its mean position. Reason (R): In simple harmonic motion the acceleration is proportional to the displacement from the mean position and is directed towards it, a = −ω²x.
Show answer

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. Since a = −ω²x, the acceleration vanishes exactly where x = 0, so R explains A. (The speed there is maximum, but that does not matter for a.)

Question 2
Assertion (A): The kinetic energy of a particle in simple harmonic motion of period T varies periodically with period T/2. Reason (R): The total mechanical energy of a harmonic oscillator is independent of time.
Show answer

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true. A holds because K = ½kA² sin²(ωt + φ) repeats when ωt changes by π: the sign of v does not matter. R is the conservation of E = ½kA², which does not tell why K repeats in T/2; so R does not explain A.

Take the free Class 11 Physics testSee the Class 11 flashcards

← Chapter 12: Kinetic TheoryChapter 14: Waves →