In Rutherford's scattering experiment, if impact parameter b = 0, then the value of the scattering angle will be:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 180°
The impact parameter b is the perpendicular distance of the initial velocity vector of the α particle from the centre of the nucleus. For \( b = 0 \) the particle is aimed straight at the nucleus (a head-on collision), so it is stopped by the Coulomb repulsion and retraces its path. It is scattered back through \( 180^\circ \).
NCERT (2026-27):
Alpha-Particle Trajectory – “… 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). … In case of head-on collision, the impact parameter is minimum and the α-particle rebounds back (θ ≅ π).”
