A negatively charged plate has charge density of $2 \times 10^{-6} \mathrm{C} / \mathrm{m}^2$ . The initial distance of an electron which is moving toward plate, cannot strike the plate, if it is having energy of 200 eV
Text Solution
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Let an electron is projected towards the plate from the r distance as shown in fig.
It will not strike the plate if and only if KE ≤ ≤ e(E ⋅ ⋅ r) (where E = Electric field due to charge plate $= \frac{\sigma}{2 \epsilon_0}$ )
⇒ ⇒ $r \geq \frac{KE}{e\sqrt{E}}$ . Hence minimum value of r is given by
$r = \frac{KE}{eE} = \frac{200 \text{ eV}}{e \times \frac{\sigma}{2 \varepsilon_0}}$ $\frac{400 \times 8.86 \times 10^{-12}}{2 \times 10^{-6}} = 1.77 \, mm$
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