Question

Two infinite planes of charge lie parallel to each other and to the yz plane. One is at x = -5 m and has a surface charge density of σ = -2.6 µC/m^2. The other is at x = 3 m and has a surface charge density of σ = 5.8 µC/m^2. Find the electric field for the following locations. (a) x < -5 m
(b) -5 m < x < 3 m
(c) x > 3 m

Answer 1

Answer:

a) -180.7 kN/C

b) -474.3 kN/C

c) 180.7 kN/C

Explanation:

For infinite planes the electric field is constant on each side, and has a value of:

E  = σ / (2 * e0) (on each side of the plate the field points in a different direction, the fields point towards positive charges and away from negative charges)

The plate at -5 m produces a field of:

E1 = 2.6*10^-6 / (2 * 8.85*10^-12) = 146.8 kN/C into the plate

The plate at 3 m:

E2 = 5.8*10^-6 / (2 * 8.85*10^-12) = 327.5 kN/C away from the plate

At x < -5 m the point is at the left of both fields

The field would be E = 146.8 - 327.5 = -180.7 kN/C

At -5 m < x < 3 m, the point is between the plates

E = -146.8 - 327.5 = -474.3 kN/C

At x > 3 m, the point is at the right of both plates

E = -146.8 + 327.5 = 180.7 kN/C