Question

A long straight wire carries 10 $A \,d.c$. current an electron travels perpendicular to the plane of this wire at a distance $0.1\, m$ with velocity $5.0 \times10^6 m \,s^{-1}$. Force acting on the electron due to current in wire is

• A. zero N
• B. $0.6 \times10^{-17} N$
• C. $2.4 \times10^{-17} N$
• D. $2.2 \times10^{-17} N$

Answer 1

Answer: (A)

zero N

Answer 2

Force on the electron $\vec{F}=-e\left(\vec{v} \times\vec{B}\right)$. As electron is travelling in a plane perpendicular to the plane of wire, so angle ? between $\vec{v}$ and $\vec{B}$ is either 0$^{\circ}$ or 180$^{\circ}$ and sin 0$^{\circ}$ or sin 180$^{\circ}$ = 0.