Magnetism: Force on Charge in B — Numerical MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

Timer-based practiceDetailed answer reviewMobile-friendly flow

Force on Charge in B — NumericalMediumQuestion 20240

Question

An α-particle (charge 2e, mass 4u) moves at 10⁶ m/s perpendicular to B = 0.5 T. Its radius in meters (e = 1.6×10⁻¹⁹, u = 1.67×10⁻²⁷) is:

A
0.084 m
Correct
B
0.042 m
C
0.167 m
D
0.21 m

Correct answer

0.084 m

Explanation

r = mv/(qB) = (4×1.67×10⁻²⁷×10⁶)/(2×1.6×10⁻¹⁹×0.5) = 6.68×10⁻²¹/(1.6×10⁻¹⁹) ≈ 0.0418 m ≈ 0.042 m. (r ≈ 0.042 m is correct; 0.084 m would be for full circle diameter.)

Review Magnetism notes Start timed chapter practice