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Q. Two charged thin infinite plane sheets of uniform surface charge density $σ_+$ and $σ_-$, where $|σ_+| > |σ_-|$, intersect at right angles. Which of the following best represents the electric field lines for this system? Source (pg 4)

My thoughts: The component of the field due to $σ_+$ will be more than $σ_-$ leading to something like in fig 4. And, the field lines will be perpendicular when they are close to the plates (like in fig 3). But none of the options seem to satisfy both.

What's wrong?

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Try to divide the problem in 4 quadrants and find the direction of the electric field in each of these 4. Use the superposition principle of the electric field to find the field produced by the two charged plates.

If you know the direction of the field produced by the positively charged plate and the field produced by the negatively charged plate, sum the two as vectors and you get your answer.

To decide between two possible solutions, make use of the magnitude of the surface charge density.

Hope it helps ;)

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  • $\begingroup$ Here's what I get. $\endgroup$
    – Shub
    Commented Apr 23, 2022 at 18:03
  • $\begingroup$ Great ! I agree with the fact that field lines have to be perpendicular to equipotential surfaces. But maybe the "best represents" in the text means something. Option 4 has to be the best one :) $\endgroup$
    – MauvaiseFoi
    Commented Apr 24, 2022 at 8:06

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