Assertion (A) & Reason (B) MCQ

Question 11 Mark

Assertion (A): If the distance between parallel plates a capacitor is halved and dielectric constant is made three times then the capacitance becomes six times.
Reason (R) : Capacitance of the capacitor does not depend upon the nature of the material of the plates of the capacitor.

Answer

(b): Assertion and reason both are correct statements but reason is not correct explanation for assertion.
Explanation: Assertion and reason both are correct statements but reason is not correct explanation for assertion.

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Question 21 Mark

Assertion (A) : The quantity L/R possesses the dimension of time.
Reason (R): In order to reduce the rate of increase of current through a solenoid, we should increase the time constant.

Answer

(c): A is true but R is false
Explanation: $I=\frac{\varepsilon}{R}=\frac{L}{R} \frac{d I}{d t}$
or $\left[\frac{L}{R}\right]=I \cdot \frac{d t}{d I}=\frac{[I] T T]}{[I]}=[ T ]$
$\therefore A$ is true but $R$ is false.
In order to reduce the rate of increase of current through the solenoid, we increase time constant ( ). But L is given to be constant, so we use a high resistance R in series with it.

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Question 31 Mark

Assertion (A) : Wavefront emitted by a point source of light in an isotropic medium is spherical.
Reason (R): Isotropic medium has same refractive index in all directions.

Answer

(a): Both A and R are true and R is the correct explanation of A.
Explanation: If a medium has same refractive index at every point in all directions, then the wavefront obtained from a point source in such a medium is spherical since wave travels in all direction with same speed. Such a medium is known as isotropic medium. So, the assertion and reason both are true and the reason explains the assertion properly.

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Question 41 Mark

Assertion (A): In process of photoelectric emission, all emitted electrons do not have same kinetic energy.
Reason (R): If radiation falling on the photosensitive surface of metal consists of different wavelengths then energy acquired by electrons absorbing photons of different wavelengths shall be different.

Answer

(b): Both A and R are true but R is not the correct explanation of A.
Explanation: Both statement are true; but even it radiation of single wavelength is incident on photosensitive surface, electrons of different KE will be emitted.

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Physics Assertion (A) & Reason (B) MCQ

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