Question 85: EM waves

Question

A velocity selector consists of electric field $$\vec{E}=E \,\hat{k}$$ and magnetic field $$\vec{B}=B \,\hat{j}$$ with $$B=12 \,m T$$. The value of $$E$$ required for an electron of energy $$728 \,\mathrm{e} V$$ moving along the positive $$x$$-axis to pass undeflected is :
(Given, mass of electron $$=9.1 	imes 10^{-31} \mathrm{~kg}$$ )

Accepted Answer

$$v = {E \over B}$$ and $$K = {1 \over 2}m{v^2}$$
$$ \Rightarrow \sqrt {{{2K} \over m}}  	imes B = E$$
$$ \Rightarrow E = \sqrt {{{2 	imes 728 	imes 1.6 	imes {{10}^{ - 19}}} \over {9.1 	imes {{10}^{ - 31}}}}}  	imes 12 	imes {10^{ - 3}}$$
$$ = 192000$$ V/m

Answer

$$192 \,\mathrm{kVm}^{-1}$$

Answer

$$192 \,\mathrm{mVm}^{-1}$$

Answer

$$9600 \,\mathrm{kVm}^{-1}$$

Answer

$$16 \,\mathrm{kVm}^{-1}$$

EM waves

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