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- Thread starter jyothsna pb
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A simple explanation: The electric field of a point charge is inversely proportional to r^2. For a line charge, it is infinite in one of the directions so you will never be far enough away from it to observe the 1/r^2, but you can observe the 1/r. You are basically replacing one of the r's with L, and then you have Q/L = [itex]\lambda[/itex] (charge per unit length).

For a 2d sheet, it is infinite in 2 directions. So that completely cancels out the 1/r^2 and you are left with a constant. Or replacing both r's in r^2 with A = area to get [itex]Q/A = \sigma[/itex] (charger per unit area).

This is a very basic explanation.

For a 2d sheet, it is infinite in 2 directions. So that completely cancels out the 1/r^2 and you are left with a constant. Or replacing both r's in r^2 with A = area to get [itex]Q/A = \sigma[/itex] (charger per unit area).

This is a very basic explanation.

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So you have a 2D poisson equation for a point charge. This ends up giving you a 1/r term for the electric field. So the infinite line charge acts like a point charge in 2 dimensions.

You can do the same for an infinite sheet charge in the x-y plane, by taking a 1D space in the z-direction and saying it is periodic in the x and y-directions. Solve for the E-field in 1D space, you get a constant. So an infinite sheet charge acts like a point charge in 1 dimension.

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thanks 4 d reply

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