Question

The electric field in a region is uniform and directed in the −x direction as shown by the gray arrow in the diagram below. The magnitude of this field is 300 N/C. The (x, y) coordinates of A, B, and C are as follows: A = (2.2, 7.5) m; B = (2.2, −1.2) m; C = (−0.5, 0.8) m.

(a) What is the work done in moving a positive charge q = 11 nC from B to A?

(b) What is the work done in moving a positive charge q = 11 nC from C to A?

Answer 1

Electric field is uniform,

force on the charge   F = Eq,

as the field is uniform and the force is const. work done

Eqs , s- the displacement.

a) B - (2.2, -1.2) , A : (2.2, 7.5)

The field is dorected in -x direction, hence work is done only with x-displacement, no work is done with y-displacement

W = 300*11E-9*(2.2- 2.2) = 0

0, displacement in the field direction and now work is done on the charge by the electrid field

b) C: (-0.5, 0.8) , A : (2.2 ,7.5)

W = 300*11E-9 * (-0.5 - 2.2) = -8.91E-6 J

-ve sign indicates external work is done on the charge which moves oppiste to the direction of the field and the electric force.