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Physics Assertion (A) & Reason (B) MCQ

MODEL PAPER 2 · 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): If a proton and electron are moving with same velocity, then wavelength of de-Broglie wave associated with electron is longer than that associated with proton.
Reason (R): The wavelength of de-Broglie wave associated with a moving particle is inversely proportional to its mass.
Answer
(a) Both A and R are true and R is the correct explanation of A.
Explanation: $\lambda=\frac{h}{m v}$
Both proton and electron are moving with same velocity. So, $\lambda \propto \frac{1}{m}$. So, the reason is true.
So, wavelength of electron > wavelength of proton. So, the assertion is true and reason is the proper explanation of the assertion.
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Question 21 Mark
Assertion: A parallel plate capacitor is connected across battery through a key. A dielectric slab of dielectric constant K is introduced between the plates. The energy which is stored becomes K times.
Reason(R): The surface density of charge on the plate remains constant or unchanged.
Answer
(c) Assertion is correct statement but reason is wrong statement. .
Explanation: Assertion is correct statement but reason is wrong statement.
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Question 31 Mark
Assertion (A): A bulb connected in series with a solenoid is connected to ac source. If a soft iron core is introduced in the solenoid, the bulb will glow brighter.
Reason (R): On introducing soft iron core in the solenoid, the inductance increases.
Answer
(d) A is false but R is true.
Explanation: A is true but R is false.
On introducing soft iron core, the bulb will glow dimmer. This is because on introducing soft iron core in the solenoid, its inductance L increases, the inductive reactance, $X _{ L }=\omega L$ increases and hence the current through the bulb decreases.
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Question 41 Mark
Assertion (A): In Young's double slit experiment the fringes become indistinct if one of the slits is covered with cellophane paper.
Reason (R): The cellophane paper decreases the wavelength of light.
Answer
(c) A is true but R is false.
Explanation: A is true but R is false.
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