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નીચેની આકૃતિ $XY$ સમતલમાં વિદ્યુતક્ષેત્ર માટે બે સમસ્થિતિમાન રેખાઓ બતાવે છે. સ્કેલ દર્શાવ્યો છે અવકાશમાં મસસ્થિતિમાન રેખાઓ વચ્ચે વિદ્યુતક્ષેત્રનો $X$ - ઘટક $E_x$ અને $Y$ - ઘટક $E_y$ છે. અનુક્રમે ........ છે.

$+100 V/m, -200 V/m$
$+200 V/m, +100 V/m$
$-100 V/m, +200 V/m$
$-200 V/m, -100 V/m$
Solution
The parallel equipotential lines represent presence of a uniform Electric field in the region.
Electric field will be E perpendicular to the equipotential surfaces as shown in figure.
Slope of equipotential surfaces,
$\tan \theta=\frac{1-0}{4-2}=\frac{1}{2}$
$\Rightarrow \sin \theta=\frac{1}{\sqrt{5}} \text { and } \cos \theta=\frac{2}{\sqrt{5}}$
Here, potential difference $\Delta V=2$ volt
Along the direction of Electric field.
Distance between two equipotential lines, $d=0.02 \sin \theta=\frac{0.2}{\sqrt{5}}$
Using, $\Delta V = Ed$ we have,
$2=E \times \frac{0.02}{\sqrt{5}}$
$\therefore E =100 \sqrt{5}\,V / m$
From the geometry shown in figure,
$E_x=-E \sin \theta=-100 \sqrt{5} \times \frac{1}{\sqrt{5}}$
$\therefore E_x=-100\,V / m$
similary,
$E_y=E \cos \theta=100 \sqrt{5} \times \frac{2}{\sqrt{5}}$
$\therefore E_y=200\,V / m$
Hence, option $(c)$ is the correct answer.
Why this question?
In such questions the parallel equipotential surface gives hint for uniform $\vec{E}$.
for which we can apply $\Delta V = Ed$ and distance between equipotential surface
$(d)$ in direction of $\vec{E}$ can be calculated by observing geometry.