Physics - Magnetism Question with Solution | TestHub

Fiven that $\overrightarrow{E}=E\hat{\mathrm{k}}$ and $\overrightarrow{B}=12 \hat{\mathrm{j}} \mathrm{mT}$

Kinetic energy$=728 \mathrm{eV}$

Kinetic energy $=\frac{1}{2}m{v}^2$

$\Rightarrow 728 \mathrm{eV}=\frac{1}{2}\times 9.1\times {10}^{-31}\times v^2$

$\Rightarrow 728\times 1.6\times {10}^{-19}=\frac{1}{2}\times 9.1\times {10}^{-31}\times v^2$

$\Rightarrow v=16\times {10}^6 \mathrm{m} {\mathrm{s}}^{-1}$

For electron to move undeflected net force on it should be zero.

$\Rightarrow eE=evB$

$\Rightarrow E=vB=16\times {10}^6\times 12\times {10}^{-3}$

$\Rightarrow E=192\times {10}^3 \mathrm{V} {\mathrm{m}}^{-1}=192 \mathrm{kV} {\mathrm{m}}^{-1}$