Physics problem

Question

An electric force is formed by a charged particle q=1.5•10^(-9)C, (1.5 times 10 in the exponent -9).In what distance are placed two equalpotencial areas in vacuum, if their potentials are φ1=45 V and φ2=30 V?

Answer 1

First, a clarification:  The charge q establishes an electric potential, and hence an electric field, but not a force.  You need a second charge at some finite distance from q in order to establish a force.

 

Regarding the equipotential surfaces:  They must both be spheres centered at the location of q.

 

φ(r) = kq/r ⇒

 

r = kq/φ

 

r₁ = kq/φ₁ = (9 x 10⁹)(1.5 x 10^-9)/45 m = ? m

 

r₂ = kq/φ₂ = (9 x 10⁹)(1.5 x 10^-9)/30 m = ? m