In Rutherford's α – particle scattering experiment, the angle of scattering suffered by α – particle
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → decreases with the increase in the impact parameter.
The impact parameter b is the perpendicular distance of the initial line of motion of the α-particle from the centre of the nucleus. A particle aimed close to the nucleus feels a strong repulsion and is deflected through a large angle; a head-on particle (b = 0) bounces straight back (θ = 180°).
\( \displaystyle b \propto \cot\frac{\theta}{2} \)
As b increases, \( \cot(\theta/2) \) increases, so the scattering angle decreases.
NCERT (2026-27):
Alpha-Particle Trajectory – “The trajectory traced by an α-particle depends on the impact parameter, \( b \) of collision. The impact parameter is the perpendicular distance of the initial velocity vector of the α-particle from the centre of the nucleus (Fig. 12.4). … It is seen that an α-particle close to the nucleus (small impact parameter) suffers large scattering. … For a large impact parameter, the α-particle goes nearly undeviated and has a small deflection (\( \theta \cong 0 \)).”
