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Physics Assertion (A) & Reason (B) MCQ

MODEL PAPER 8 · Rajasthan Board (RBSE) STD 12 Science (Rajasthan - English Medium). 4 questions.

Questions

Assertion (A) & Reason (B) MCQ

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4 questions · self-marked practice — reveal the answer and mark yourself.

Question 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.
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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Question 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.
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 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.
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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Question 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
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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