Two infinitely large parallel plane sheets carry uniform surface charge densities +σ and -2σ, as shown in the original figure. A point charge +q is placed midway between them. The magnitude of the force on the charge is:

Question

G1 Physics · Accepted Answer

The electric field of an infinite sheet of surface charge density σ is E = |σ|/(2ε₀). Between the +σ sheet and the -2σ sheet, the field due to +σ points away from the positive sheet and the field due to -2σ points toward the negative sheet. Hence both fields are in the same direction and add. E = σ/(2ε₀) + 2σ/(2ε₀) = 3σ/(2ε₀). Force magnitude on +q: F = qE = 3σq/(2ε₀). Correct option: C.