# field of an infinite sheet

#### curious_to_know

Joined Jun 23, 2007
9
How to derive the expression of the field of infinite charged sheet of σ using the expression of a infinite line charge ?

if the expression of field of an infinite line charge is given by

$$\frac{\lambda}{2\pi\epsilon r}$$

where r is the distance of the 'test charge' from the line.

and λ the linear charge density of the line

#### mik3

Joined Feb 4, 2008
4,843
Imagine a small surface above the plate and use Gauss law to find E at the point distance over the plate.

#### steinar96

Joined Apr 18, 2009
239
Apply an cylindrical gaussian surface so that the axis of the cylinder is perpendicular to the plane. The electric flux will be zero trough the sides but positive trough the top and bottom of the cylinder. From that you can calculate your answer

#### curious_to_know

Joined Jun 23, 2007
9
well thnx guys for that help..well i wud say its an easy way out and after all thats not my homework...my homework is to DERIVE the expression from the given data..from the expression of a line charge(infinite)

so plz reply accordingly..

#### steinar96

Joined Apr 18, 2009
239
You just got the info needed to derive the expression or at least point you in the right direction. Is it not what you asked for. The method used to derive the expression involves picking an appropriate gaussian surface and applying gauss's law.

Your homework is to derive the expression. We are propably doing you a favor by pointing you in the right direction without solving the proplem for you