Assertion (A): When a pulse on string reflects from free end, the resultant pulse is formed in such a way that slope of string at free end is zero.
Reason (R): Zero resultant slope ensures that there is no force component perpendicular to string.
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
At a free end, there's no transverse force, so the slope \( \frac{\text{dy}}{\text{dx}} = 0 \). The resultant pulse is formed such that the free end is a displacement antinode. This implies zero slope, ensuring no transverse force. Both Assertion and Reason are true, and R correctly explains A.
Assertion (A): The pitch of wind instruments rises and that of string instruments falls as an orchestra warms up.
Reason (R): When temperature rises, speed of sound in air increases but speed of wave in a string fixed at both ends decreases.
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
For wind instruments, pitch \( f \) is proportional to the speed of sound in air \( v_{\text{air}} propto \sqrt{T_{\text{temp}}} \). As temperature rises, \( v_{\text{air}} \) increases, so pitch rises. For string instruments, \( f propto v_{\text{string}} = \sqrt{T_{\text{tension}}/\mu} \). As temperature rises, the string expands, reducing tension \( T_{\text{tension}} \), so \( v_{\text{string}} \) decreases and pitch falls. Reason R accurately explains this behavior for both cases.
Assertion (A): Sound travels faster on a rainy day than on a dry day.
Reason (R): With increase in humidity pressure increases.
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 \( v = \sqrt{\gamma P/\rho} \). Moist air (humid air) has a lower average molecular mass and thus lower density \( \rho \) than dry air at the same pressure and temperature. A lower density leads to a higher speed of sound. Thus, A is true. Reason R is false; increasing humidity does not necessarily increase total pressure, and the primary factor for faster sound is reduced density.
Assertion (A): Node of pressure wave is formed at the open end of an organ pipe.
Reason (R): Reflected pressure wave from an open end will have phase difference of \( \pi \) w.r.t. to the incident pressure wave.
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
At the open end of an organ pipe, the pressure is approximately atmospheric pressure, meaning there is no excess pressure variation, hence it is a pressure node. When a pressure wave reflects from an open end (a boundary to a less dense medium), it undergoes a \( \pi \) (180 degrees) phase shift. This phase shift causes the incident and reflected waves to destructively interfere at the open end, creating a pressure node. Both A and R are true, and R explains A.
Assertion (A): When a wave enters from one medium to another, its frequency is not changed.
Reason (R): Speed of a wave in a medium is property of the source.
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 frequency of a wave is determined by the source that generates it and remains constant as the wave propagates from one medium to another. The speed of a wave, however, is a characteristic property of the medium it is traveling through, not the source. Thus, Assertion A is true, but Reason R is false.
Assertion (A): Two waves moving in a uniform string having uniform tension cannot have different velocities.
Reason (R): Elastic and inertial properties of string are same for all waves in same string. Moreover, velocity of wave in a string depends on its elastic and inertial properties only.
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 a transverse wave on a string is given by \( v = \sqrt{T/\mu} \), where \( T \) is the tension (elastic property) and \( \mu \) is the linear mass density (inertial property). If the string is uniform (constant \( \mu \)) and has uniform tension (constant \( T \)), then \( v \) must be constant for all waves propagating on it. Both A and R are true, and R correctly explains A.
Assertion (A): Two sound waves of same intensity in a particular medium will have displacement amplitude in ratio of 2:1 if they have frequency in the ratio 1:2.
Reason (R): Two wave of same velocity and amplitude in a particular medium have equal intensity.
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
Intensity of a sound wave is \( I = \frac{1}{2} \rho v \omega^2 A^2 \), where \( \omega = 2\pi f \). If \( I_1 = I_2 \) and the medium is the same (so \( \rho \) and \( v \) are constant), then \( \omega_1^2 A_1^2 = \omega_2^2 A_2^2 \). Given \( f_1 : f_2 = 1 : 2 \), so \( \omega_1 : \omega_2 = 1 : 2 \). This yields \( (1)^2 A_1^2 = (2)^2 A_2^2 \), so \( A_1^2 = 4 A_2^2 \), meaning \( A_1 : A_2 = 2 : 1 \). Thus, A is true. Reason R is false because intensity also depends on frequency (\( \omega \)), so waves with the same velocity and amplitude but different frequencies will have different intensities.
Assertion (A): Every small part of string does SHM in sinusoidal travelling wave.
Reason (R): In this small segment of string total energy is conserved.
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
In a sinusoidal traveling wave, each particle of the string oscillates in simple harmonic motion (SHM) perpendicular to the direction of wave propagation. So, Assertion A is true. However, for a *traveling* wave, energy is continuously transmitted along the string. Therefore, the total energy within a small segment of the string is *not* conserved, as energy flows into and out of the segment. Reason R is false.
Assertion (A): If two waves of same amplitude produce a resultant wave of same amplitude, then the phase difference between them will be \(120^\circ\).
Reason (R): The resultant amplitude of two waves is equal to sum of amplitude of two waves.
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
For two waves of amplitude \(A\) and phase difference \(phi\), the resultant amplitude is \(A_r = 2A \cos(\frac{\phi}{2})\). Given \(A_r = A\), so \(A = 2A \cos(\frac{\phi}{2})\), which means \(cos(\frac{\phi}{2}) = \frac{1}{2}\). Thus \(\frac{\phi}{2} = 60^\circ\), so \(\phi = 120^\circ\). Hence (A) is true. The resultant amplitude is the sum only if \(\phi = 0\). So (R) is false.
Assertion (A): In a sinusoidal travelling wave on a string potential energy of deformation of string element at extreme position is maximum.
Reason (R): The particles in sinusoidal travelling wave perform SHM.
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
In a wave, potential energy is stored due to deformation (strain). At extreme positions (maximum displacement), the deformation is maximum, leading to maximum potential energy. So (A) is true.
Particles in a transverse wave undergo simple harmonic motion. So (R) is true. However, (R) does not explain why potential energy is maximum at extreme positions; it's a general characteristic of the particle motion. Therefore, (R) is not the correct explanation of (A).