An electron initially at rest, is accelerated through a potential… - Vidyadip

MCQ

An electron initially at rest, is accelerated through a potential difference of $ 200$ volt, so that it acquires a velocity $8.4 \times {10^6}m/s.$ The value of $e/m$ of electron will be

A
$2.76 \times {10^{12}}C/kg$
✓
$1.76 \times {10^{11}}C/kg$
C
$0.76 \times {10^{12}}C/kg$
D
None of these

✓

Answer

Correct option: B.

$1.76 \times {10^{11}}C/kg$

b
(b) $\frac{1}{2}m{v^2} = eV\,\, \Rightarrow \,\,\frac{e}{m} = \frac{{{v^2}}}{{2V}} = \frac{{{{(8.4 \times {{10}^6})}^2}}}{{2 \times 200}}$$ = 1.76 \times {10^{11}}\,\frac{C}{{kg}}.$

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