Three parallel metallic plates of area A carry total charges Q₁, Q₂ and Q₃ as shown. Edge effects are negligible. Find the charge on the two outermost surfaces a and f.
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Three parallel metallic plates of area A carry total charges Q₁, Q₂ and Q₃ as shown. Edge effects are negligible. Find the charge on the two outermost surfaces a and f.

G1 Physics · Accepted Answer

Outside a parallel stack, symmetry and Gauss's law make the fields on the two outer sides equal in magnitude. Therefore the total charge appearing on the two outermost surfaces is shared equally: qₐ=qf=(Q₁+Q₂+Q₃)/2. Correct answer: A.