CBSE Class 12 · 2009 · ElectrostaticsShort Answer

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Use Gauss's law to derive the expression for the electric field between two uniformly charged large parallel sheets with surface charge densities

σ

and

- σ

respectively.

Solution

Each infinite sheet produces a uniform field

\frac{σ}{2 ε _{0}}

on either side of it.
Let sheet I carry

+ σ

and sheet II carry

- σ

.
Between the sheets, both fields point from I to II, so they add:

E = \frac{σ}{2 ε _{0}} + \frac{σ}{2 ε _{0}} = \frac{σ}{ε _{0}}

directed from the positive sheet to the negative sheet.
In the two outer regions the fields are equal and opposite, so they cancel:

E = 0

CBSE Class 12 Board · 2009 · Subjective

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