Question

An electron having kinetic energy $10eV$ is circulating in a path of radius $0.1m$ in an external magnetic field of intensity $10^{-4}T$ . The speed of the electron will be

• A. $1.76\times \left(10^6\right){\mathrm{ms}}^{-1}$
• B. $4.8\times \left(10^6\right){\mathrm{ms}}^{-1}$
• C. $2.0\times \left(10^{12}\right){\mathrm{ms}}^{-1}$
• D. $4.8\times \left(10^{12}\right){\mathrm{ms}}^{-1}$

Answer 1

Answer: (A)

When charge enters into a perpendicular magnetic field, it starts to move in a circular path.
Radius of a circular path followed by a charge particle:
$r=\frac{mV}{qB}$
$V=1.76\times \left(10^6\right){\mathrm{ms}}^{-1}$