We cannot hear the sound of a bell ringing in a closed jar after most of the air is pumped out. Class 9

We cannot hear the sound of a bell ringing in a closed jar after most of the air is pumped out. Class 9

Question 1.

Assertion (A): We cannot hear the sound of a bell ringing in a closed jar after most of the air is pumped out. Class 9

Reason (R): Sound requires a medium to travel. (Page 188)

Choose the correct statement:

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

(ii) Both A and R are true, and R is the correct explanation of A.

(iii) A is true, but R is false.

(iv) A is false, but R is true.

Answer:

(ii) Both A and R are true, and R is the correct explanation of A.

Explanation: When air is pumped out, a near vacuum is created. Since sound is a mechanical wave requiring a medium to propagate, the absence of a medium (air) means sound cannot reach our ears, even though the bell is ringing.

Question 2.

Assertion (A): Compressions and rarefactions move through the medium. Class 9

Reason (R): Individual particles of the medium continuously move forward with the wave. (Page 191)

Choose the correct statement:

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

(ii) Both A and R are true, and R is the correct explanation of A.

(iii) A is true, but R is false.

(iv) A is false, but R is true.

Answer:

(iii) A is true, but R is false.

Explanation: Compressions and rarefactions do move through the medium. However, individual particles of the medium do not move forward with the wave - they only oscillate (vibrate) about their mean positions. It is the disturbance (energy) that travels, not the particles.