Assertion (A) & Reason (B) MCQ

MCQ 11 Mark

Assertion (A): de-Broglie wavelength is significant for microscopic particles.
Reason (R): de-Broglie wavelength is inversely proportional to the mass of a particle when velocity is kept constant.

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false.
D
A is false but R is true.

Answer

(a) Both A and R are true and R is the correct explanation of A.
Explanation: de-Broglie wavelength, $\lambda=\frac{h}{m v}$
h and v remaining constant, $\lambda \propto \frac{1}{m}$
So, as the mass of the particle becomes smaller and smaller the de-Broglie wavelength of the particle becomes more and more significant.
Hence, assertion and reason both are true and reason explains the assertion properly.

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MCQ 21 Mark

Assertion (A): An applied electric field polarises a polar dielectric.
Reason (R): The molecules of a polar dielectric possess a permanent dipole moment, but in the absence of electric field, these dipoles are randomly oriented and when electric field is applied these dipoles align along the direction of electric field.

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false
D
A is false but R is true.

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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MCQ 31 Mark

Assertion (A): Light from two coherent sources is reaching the screen. If the path difference at a point on the screen for yellow light is $\frac{3 \lambda}{2}$, then the fringe at that point will be coloured.
Reason (R): Two coherent source always have constant phase relationship.

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false
D
A is false but R is true.

Answer

(d) A is false but R is true.
Explanation: When the source is emitting yellow light, then there will be a dark fringe at a point where path difference is $\frac{3 \lambda}{2}$ [from condition for dark fringe $x=(2 n+1) \frac{\lambda}{2}$ ]. If the light is white then the fringe will be coloured, the yellow and neighbouring colours being absent.

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MCQ 41 Mark

Assertion (A): At resonance, the inductive reactance is equal and opposite to the capacitive reactance.
Reason (R): In series LCR-circuit, the inductive reactance is equal and opposite to the capacitive reactance

A
Both A and R are true and R is the correct explanation of A.
B
Both A and R are true but R is not the correct explanation of A.
C
A is true but R is false.
D
A is false but R is true.

Answer

(c) A is true but R is false.
Explanation: In a series LCR-circuit, only at resonance, the inductive reactance is equal and opposite to the capacitive reactance.

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Physics Assertion (A) & Reason (B) MCQ

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