Suppose a uniform electric field of 4 N/C is in the positive x direction. When a charge is placed at and fixed to the origin, the resulting electric field on the x axis at x = 2 m becomes zero. What is the magnitude of the electric field at x = 4 m on the x axis at this time?
A) 0
B) 1 N/C
C) 2 N/C
D) 4 N/C
E) More information is needed to find the resulting field magnitude at this position.

Question

Quizplus · Accepted Answer

The charge at the origin creates an electric field that cancels the uniform field at x = 2 m. This means the charge's field is -4 N/C at x = 2 m. The field from a point charge decreases with the square of the distance, so at x = 4 m, it will be -1 N/C. The uniform field is 4 N/C, so the net field is 4 N/C - 1 N/C = 3 N/C.

Suppose a Uniform Electric Field of 4 N/C Is in the Positive