Assertion (A): Sound travels faster in air than in water.
Reason (R): Air is always rarer medium with respect to water medium.
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 false; sound travels much faster in water (approx. \(1480 \text{ m/s}\)) than in air (approx. \(343 \text{ m/s}\)). Reason (R) is true; air is indeed a rarer (less dense) medium than water. Given that Assertion (A) is false, option 4 is the only choice that fits this condition among the provided options, despite Reason (R) being true.
Assertion (A): Sound waves cannot propagate through vacuum but light waves can.
Reason (R): Sound waves cannot be polarised but light waves can be.
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 because sound waves are mechanical and require a medium, whereas light waves are electromagnetic and can propagate in vacuum.
Reason (R) is true as sound waves are longitudinal and cannot be polarised, while light waves are transverse and can be polarised. However, the ability to polarise is unrelated to propagation through a vacuum.
Thus, (R) is not the correct explanation of (A).
Assertion (A): Interference is position dependent phenomenon.
Reason (R): Beats is time dependent phenomenon.
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
Interference describes the variation of intensity with position due to superposition of waves, so (A) is true. Beats describe the periodic variation in intensity with time at a point due to superposition of two waves with slightly different frequencies, so (R) is true. (R) does not explain (A).
Assertion (A): An acoustic guitar depends for its sound on the acoustic resonance produced in the hollow body of the instrument by the oscillations of the strings.
Reason (R): Electric guitar is a solid instrument that based upon resonance. (In electric guitar the oscillations of the metal strings are sensed by electric “pickups” that send it to an amplifier).
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
An acoustic guitar uses the resonance of its hollow body to amplify and shape the sound produced by vibrating strings, so (A) is true. An electric guitar, being a solid-body instrument, generates sound via electromagnetic pickups sensing string vibrations, which are then amplified electronically. It does not rely on acoustic body resonance for sound production. Thus, Reason (R) is false.
Assertion (A): When two tuning fork of frequency \(256 \text{ Hz}\) and \(324 \text{ Hz}\) are vibrating together. Beats will not be heard.
Reason (R): Superposition of sound waves is possible for all frequencies of sound.
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
The beat frequency is \(|256 - 324| = 68 \text{ Hz}\) . Since this is much greater than \(10 \text{ Hz}\) , distinct beats cannot be heard. Thus, (A) is true. The principle of superposition holds for all sound waves irrespective of their frequency, so (R) is true. However, (R) does not explain (A).
Assertion (A): In a stationary-wave system, displacement nodes are pressure antinodes, and displacement antinodes are pressure nodes.
Reason (R): When a closed organ pipe vibrates, the pressure of the gas at the closed end remains constant.
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
In a stationary wave, displacement nodes correspond to points of maximum pressure variation (pressure antinodes) and displacement antinodes correspond to points of minimum pressure variation (pressure nodes). So, (A) is true.
At the closed end of an organ pipe, there must be a displacement node, which is a pressure antinode, meaning there is maximum pressure variation, not constant pressure. Thus, (R) is false.
Assertion (A): When two vibrating tuning forks having frequencies \(240 \text{ Hz}\) and \(300 \text{ Hz}\) are held near each other, beats cannot be heard by us.
Reason (R): This is because beats cannot be distinctly heard due to the property of persistence of hearing.
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
The beat frequency is \(|240 - 300| = 60 text{ Hz}\) . For distinct beats to be heard, the beat frequency should be less than \(10 text{ Hz}\) . Thus, Assertion (A) is true. Persistence of hearing is not the reason for inability to hear distinct beats; it's the ear's inability to follow rapid amplitude changes. Thus, Reason (R) is false.
Assertion (A): In a harmonic wave of a given frequency all particles have the same amplitude but different phases at a given time.
Reason (R): In a stationary wave, all particles have the same phase at a given instant but have different amplitudes.
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
In a harmonic traveling wave, all particles oscillate with the same amplitude but their phases vary with position. So, (A) is true. In a stationary wave, particles between two successive nodes vibrate in phase, but particles on either side of a node are \(180^\circ\) out of phase. Their amplitudes also vary with position. So, (R) is false.
Assertion (A): Interference can happen in sound waves.
Reason (R): In Quincke’s tube, interference is present due to initial phase difference as well as the phase difference due to path difference.
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
Sound waves, being waves, exhibit interference. Thus, Assertion (A) is true. In Quincke's tube, interference is primarily due to path difference. An initial phase difference is not typically considered in a standard setup. Therefore, Reason (R) is false.
Assertion (A): When we start filling an empty bucket with water, the pitch of sound produced goes on decreasing.
Reason (R): The frequency of man voice is usually higher than that of woman.
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
As water fills a bucket, the air column length decreases, increasing the resonant frequency and thus the pitch. So, Assertion (A) is false. The average frequency of a man's voice is lower than a woman's voice. So, Reason (R) is also false.