NCERT Class XII Chapter
Electric Charges and Fields
Questions With Solutions

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Question : 18
Total: 34
A point charge +10 μC is at a distance of 5 cm directly above the centre of a square of side 10 cm, as shown in figure. What is the magnitude of the electric flux though the square?

Solution:  
Let us assume that the given square be one face of the cube of edge 10 cm.
As charge of +10 μC is at a distance of 5 cm above the centre of a square, so it is enclosed by the cube.
Hence by Gauss’s theorem, electric flux linked with the cube is

ϕ =
q
ε0
=
10×106
8.85×1012
= 1.13 × 106 N m2C1
So, the magnitude of the electric flux through the square is
ϕsq =
ϕ
6
=
1.13
6
× 106 or ϕsp = 1.9 × 105 N m2C1
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