Assertion (A): Speed of longitudinal wave in solid and liquid is higher than gases.
Reason (R): Modulus of elasticity is more for solids as compared to liquid & gas.
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
The speed of longitudinal waves is given by \(v = \sqrt{\frac{B}{\rho}}\), where \(B\) is the bulk modulus. Solids and liquids have significantly higher bulk moduli compared to gases. Thus, longitudinal waves travel faster in solids and liquids. Both assertion and reason are true, and the reason correctly explains the assertion.
Assertion (A): The velocity of sound decreases with increase in humidity.
Reason (R): Velocity of sound does not depend on 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
The velocity of sound increases with humidity because humid air is less dense than dry air. So, Assertion (A) is false. The velocity of sound absolutely depends on the properties of the medium (density, elasticity). So, Reason (R) is also false. Both (A) and (R) are false.
Assertion (A): The change in air pressure, effect the speed of sound at constant temperature.
Reason (R): The speed of sound in a gas is directly proportional to pressure.
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
The speed of sound in a gas is \(v = \sqrt{\frac{\gamma RT}{M}}\). At constant temperature (\(T\)), the velocity is independent of pressure. So, Assertion (A) is false. Also, the speed of sound is not directly proportional to pressure. So, Reason (R) is false. Both (A) and (R) are false.
Assertion (A): When there is no relative velocity between source and observer then observed frequency is same as emitted.
Reason (R): Velocity of sound is zero when there is no relative velocity between source and observer.
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
According to the Doppler effect, the observed frequency matches the emitted frequency only when there is no relative motion between the source and observer. So, Assertion (A) is true. The velocity of sound is a property of the medium and is non-zero in an ideal medium, irrespective of relative motion between source and observer. So, Reason (R) is false. Thus, (A) is true but (R) is false.
Assertion (A): A (80 \text{ dB}) sound has twice the intensity of a \(40 \text{ dB}\) sound.
Reason (R): Loudness of a sound of a certain intensity (‘I’) is defined as \(L = 10 log_{10} left(frac{I}{I_0}right)\).
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. An 80 dB sound has an intensity \(10^4\) times greater than a \(40 \text{ dB}\) sound, not twice. Reason (R) is true as it correctly defines loudness in decibels.
Since (A) is false and (R) is true, and the option for 'A is false, R is true' is not provided, option (4) is selected as it states (A) is false.
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): 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): Sound waves can be used to explore the soft tissue of the human body.
Reason (R): Oscillations in the real world are usually damped.
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
Ultrasound, a type of sound wave, is extensively used in medical imaging to view soft tissues, making Assertion (A) true. All real-world oscillations experience damping due to dissipative forces, so Reason (R) is true. However, (R) does not explain (A).
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).