Question

A light beam travelling in the x-direction is described by the electric field $E_y=\left(300V{m}^{-1}\right)sin\omega (t-x/c).$ An electron is constrained to move along the y-direction with a speed of $2.0\times {10}^7{m}^{-1}$ Find the maximum electric force and the maximum magnetic force on the electron

• A. $4.8\times {10}^{-17}N,zero$
• B. $4.2\times {10}^{-18}N,1.8\times {10}^{-8}N$
• C. $4.8\times {10}^{-17}N,3.2\times {10}^{-18}N$
• D. Zero, Zero

Answer 1

The correct option is A $4.8\times {10}^{-17}N,zero$

A light beam travelling

$E_y=\left(300V/m\right)sinw(t-x/c)$.

$V=2.0\times {10}^7{m}^{-1}$

$B_0=\frac{F_0}{C}=\frac{300}{2\times {10}^7}=150\times {10}^{-7}T$

$F_m=B_{0}qV$

$=9.1\times {10}^{-31}\times 150\times {10}^{-7}\times 2\times {10}^7$

$=2.8\times {10}^{-28}\times 2$

$=4.8\times {10}^{-17}N$

magnetic force $=0$

because they are perpendicular to each other.