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1. Electric Charges and Fields
medium
Two point charge $-q$ and $+q/2$ are situated at the origin and at the point $(a, 0, 0)$ respectively. The point along the $X$ - axis where the electric field vanishes is
A
$x = \frac{a}{{\sqrt 2 }}$
B
$x = \sqrt 2 a$
C
$x = \frac{{\sqrt 2 a}}{{\sqrt 2 - 1}}$
D
$x = \frac{{\sqrt 2 a}}{{\sqrt 2 + 1}}$
Solution

(c) Suppose the field vanishes at $a$ (distance $x$), we have
$\frac{{kq}}{{{x^2}}} = \frac{{kq/2}}{{{{(x – a)}^2}}}$ or $2{(x – a)^2} = {x^2}$ or $\sqrt 2 (x – a) = x$
or $(\sqrt 2 – 1)x = \sqrt 2 \,a$ or $x = \left( {\frac{{\sqrt 2 \,a}}{{\sqrt 2 – 1}}} \right)$
Standard 12
Physics