Question

A particle of charge +q is a distance r away from a charged flat surface and experiences a force of magnitude F pulling it toward the surface. What is the magnitude of the force exerted on a particle of charge +q that is a distance 2r from the surface?

• A. 1/8 F
• B. 1/4 F
• C. 1/2 F
• D. F
• E. 2F

Answer 1

Answer: (D)

F

The charged flat surface means a charged sheet so the field due to charge sheet is $E=\frac{\sigma }{2{ϵ}_0}$ where $\sigma$ be the surface charge density.

The force on charge particle is $F=qE=\frac{q\sigma }{2{ϵ}_0}$. Thus, it is independent on distance.

Thus, force on charge at distance $2r$ from surface will be same as before i.e $F$