Question

A particle of charge $+q$ is at distance $r$ away from a charged flat surface and experiences a force of magnitude $F$ pulling it toward the surface. Find out the magnitude of the force exerted on the same particle if it is at a distance $2r$ from the surface?

• A. $\left(1/8\right)F$
• B. $\left(1/4\right)F$
• C. $\left(1/2\right)F$
• D. $F$
• E. $2F$

Answer 1

Answer: (B)

$\left(1/4\right)F$

Force on charge $q$ at distance $r$ is ,

$F=K/r^2$ (all other quantities are constant here)

Force on charge $q$ at distance $2r$ is ,

$F^{\prime }=K/{\left(2r\right)}^2=K/4r^2$

therefore$F^{\prime }=K/4r^2=F/4$