Assertion (A) & Reason (B) MCQ

Question 11 Mark

Assertion (A): The photoelectrons produced by a monochromatic light beam incident on a metal surface have a spread in their kinetic energies.
Reason (R): The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.

Answer

(a) Both A and R are true and R is the correct explanation of A.
Explanation: Photoelectrons produced by monochromatic light have different velocities and hence different energies. Actually all the electrons do not occupy the same level of energy. So, electrons coming out from different levels have different velocities and hence different energies. So, the assertion is true. The electrons coming out from inside the metal surface, face collisions with the other atoms in the metal. So, energies become different. Hence the reason is true and it explains the assertion.

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Question 21 Mark

Assertion (A): Positive charge always moves from a higher potential point to a lower potential point.
Reason (R): Electric potential is a vector quantity.

Answer

(c) A is true but R is false.
Explanation: If two points P and Q in an electric field are separated by an infinitesimal distance $\Delta x$ and have a potential difference $\Delta V$
between them, $E =\frac{-\Delta V}{\Delta x}$. Here, negative sign implies that $\vec{E}$ has got a direction opposite to the potential gradient, i , e, in the
direction of $\vec{E}$, the potential decreases, i. e, positive charge always moves from a higher potential point to a lower potential point.

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Question 31 Mark

Assertion (A): Interference pattern is made by using yellow light instead of red light, the fringes becomes narrower.
Reason (R): In Young's double slit experiment, fringe width is given by $\beta=\frac{\lambda D }{ d }$.

Answer

(a)Both A and R are true and R is the correct explanation of A.
Explanation: Both A and R are true and R is the correct explanation of A.

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Question 41 Mark

Assertion (A): An alternating current of frequency 50 Hz becomes zero, 100 times in one second.
Reason (R): Alternating current changes direction and becomes zero twice in a cycle.

Answer

(b)Both A and R are true but R is not the correct explanation of A.
Explanation: Both A and R are true and R is the correct explanation of A.

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Physics Assertion (A) & Reason (B) MCQ

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