Assertion (A): An alpha particle is moving towards a gold nucleus. The impact parameter is maximum for the scattering angle of 180°. Reason (R): The impact parameter in an alpha particle scattering experiment does not depend upon the atomic number of the target nucleus. (A) If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A). (B) If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A). (C) If Assertion (A) is true but Reason (R) is false. (D) If both Assertion (A) and Reason (R) are false.

PhysicsCBSE Class 12 · Board exam 2024, set 55/5/1 · 1 mark · Assertion-reason

CBSE Class 12 Physics 2024: question 16

Set in the CBSE Class 12 board exam of 2024, paper 55/5/1, section A, question 16, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q16 · 1 mark · Assertion-reasonCompetency-basedAtoms

Assertion (A): An alpha particle is moving towards a gold nucleus. The impact parameter is maximum for the scattering angle of $18 0^{\circ}$ .

Reason (R): The impact parameter in an alpha particle scattering experiment does not depend upon the atomic number of the target nucleus.

(A)If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).
(B)If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).
(C)If Assertion (A) is true but Reason (R) is false.
(D)If both Assertion (A) and Reason (R) are false.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Recall the relation between impact parameter and scattering angle.

Hint 2

$b = \frac{Z e ^{2} cot ( θ /2 )}{4 π ε _{0} K}$ .

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

$b \propto Z cot (θ /2)$ ; at $θ = 18 0^{\circ}$ , $b = 0$ (head-on), the minimum, so Assertion is false.
½ mark
$b$ depends on $Z$ of the target, so Reason is also false. Option (D).
½ mark

Answer: Option (D)

Where the marks are

Both false: b = 0 at 180° and b ∝ Z (1 mark)

Revise the chapter

Chapter: Atoms (notes, formulas, where marks are lost and every past question)
Topic: Alpha-Particle Scattering and Rutherford's Model

Practise this chapterBoard-style questions from Atoms, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 55/5/1: every question, by section.

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CBSE Class 12 Physics 2024: question 16

Hints

Step-by-step solution

Revise the chapter

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