Question

A light beam is described by $E=800\sin \omega (t-\frac{x}{c})$. An electron is allowed to move normal to the propagation of light beam with a speed of $3\times {10}^7{\text{ms}}^{-1}$. What is the maximum magnetic force exerted on the electron ?

• A. $1.28\times {10}^{-21}\text{N}$
• B. $1.28\times {10}^{-18}\text{N}$
• C. $12.8\times {10}^{-17}\text{N}$
• D. $12.8\times {10}^{-18}\text{N}$

Answer 1

The correct option is C $12.8\times {10}^{-17}\text{N}$

Given: $E_0=800{\text{Vm}}^{-1},c=3\times {10}^7{\text{ms}}^{-1}$

Using $B_0=\frac{E_0}{c}=\frac{800}{3\times {10}^7}=266.7\times {10}^{-7}$

The force on the particle is,

$F=qv{B}_0=1.6\times {10}^{-19}\times 3\times {10}^7\times 266.7\times {10}^{-7}=1280.2\times {10}^{-19}=12.8\times {10}^{-17}\text{N}$