Q. A uniform magnetic field B is acting from south to north and is of magnitude $1.5\ wb/m^{2}$. If a proton having mass $= 1.7 \times 10^{- 27}kg$ and charge $= 1.6 \times 10^{- 19}C$ moves in this field vertically downward with energy $5\ MeV$, then the force acting on it will be

A) $7.4 \times 10^{12}\ N$
B) $7.4 \times 10^{- 12}\ N$
C) $7.4 \times 10^{19}\ N$
D) $7.4 \times 10^{- 19}\ N$
Explanation

(b) $F = qvB$ and $K = \frac{1}{2}mv^{2} \Rightarrow F = qB\sqrt{\frac{2k}{m}}$
$= 1.6 \times 10^{- 19} \times 1.5\sqrt{\frac{2 \times 5 \times 10^{6} \times 1.6 \times 10^{- 19}}{1.7 \times 10^{- 27}}}$
$= 7.344 \times 10^{- 12}N$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.