Assertion (A): Beats are not observed in case of light waves from two independent sources.
Reason (R): The phase difference between two light sources changes randomly.
1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer
Stable beats require coherent sources with a constant phase difference. Independent light sources have rapidly and randomly changing phase differences, making stable beats unobservable.
Thus, Assertion (A) is true, and Reason (R) is true and is the correct explanation of (A).
Assertion (A): A vibrating tuning fork sounds louder, when its stem is pressed against a desk top.
Reason (R): When a sound wave is incident on the surface of a desk, it is totally reflected.
1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
Assertion (A) is true due to forced vibrations and resonance. The desk provides a larger surface area to vibrate, increasing the loudness.
Reason (R) is false because sound waves are not totally reflected; some energy is transmitted to the desk.