Gujarati
1. Electric Charges and Fields
medium

An electron moving with the speed $5 \times {10^6}$ per sec is shooted parallel to the electric field of intensity $1 \times {10^3}\,N/C$. Field is responsible for the retardation of motion of electron. Now evaluate the distance travelled by the electron before coming to rest for an instant (mass of $e = 9 \times {10^{ - 31}}\,Kg.$ charge $ = 1.6 \times {10^{ - 19}}\,C)$

A

$7\, m$

B

$0.7\, mm$

C

$7\, cm$

D

$0.7\, cm$

Solution

(c) Electric force $qE = ma$ $==>$ $a = \frac{{QE}}{m}$
$\therefore \,a = \frac{{1.6 \times {{10}^{ – 19}} \times 1 \times {{10}^3}}}{{9 \times {{10}^{ – 31}}}} = \frac{{1.6}}{9} \times {10^{15}}$
$u = 5 \times {10^6}$ and $v = 0$
 From ${v^2} = {u^2} – 2as$ $==>$ $s = \frac{{{u^2}}}{{2a}}$
 Distance $s = \frac{{{{(5 \times {{10}^6})}^2} \times 9}}{{2 \times 1.6 \times {{10}^{15}}}}$$ = 7\,cm.({\rm{approx}})$

Standard 12
Physics

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