Q. In a region of space, the electric field is given by $ \displaystyle \vec{E} = 8\hat{i} + 4\hat{j} + 3\hat{k} $ . The electric flux through a surface of area 100 units in the xy plane is
(a) 800 units
(b) 300 units
(c) 400 units
(d) 1500 units
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Ans: (b)
Sol: $ \displaystyle \vec{E} = 8\hat{i} + 4\hat{j} + 3\hat{k} $
Area vector is
$ \displaystyle \vec{A} = 100 \hat{k} $ (As it perpendicular to XY Plane)
Electric flux
$ \displaystyle \phi = \vec{E} . \vec{A} $
$ \displaystyle \phi = (8\hat{i} + 4\hat{j} + 3\hat{k}) . (100 \hat{k}) $
= 300 unit