SAT Subject Physics Practice Question 297: Answer and Explanation
68. The electric field strength at a point some distance away from a source charge does NOT depend on
A. the magnitude of the source charge.
B. the sign of the source charge.
C. the distance from the source charge.
D. the nature of the medium surrounding the source charge.
E. None of the above
Correct Answer: B
The strength of the electric field at a point that is a distance r from a point charge of magnitude Q is given by the expression . If the source charge is surrounded by an insulating medium other than vacuum, then the value of k we use in this expression is actually , where k0 is Coulomb’s constant and K is the dielectric constant of the medium. The sign of the source charge will affect the direction of the electric field vector at a point but not the strength of the field.