CBSE Class 12 · 2024 · Modern PhysicsMultiple Choice

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.✓ Correct

Answer: (D)

Solution

The impact parameter is

b \propto cot \frac{θ}{2}

. For

θ = 18 0^{\circ}

cot 9 0^{\circ} = 0

, so

b

is minimum (zero), not maximum — Assertion is false.
Also

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

does depend on the atomic number

Z

— Reason is false.
Both A and R are false.

(D)

CBSE Class 12 Board · 2024 · Single correct option