A constant electric field of magnitude E 375 Vm points in t
     A constant electric field of magnitude E = 375 V/m points in the positive x direction. A charge Q is moved in positive x direction with the field by an external force. Correct: The sign of the work depends on the sign of the charge. Incorrect Without an external force, a free negative charge would accelerate in the direction of the depicted path. Incorrect The work required is independent of the angle of the path with respect to the field. Incorrect No work is required. Incorrect Without an external force, a free negative charge would accelerate perpendicular to the depicted path.  
  
  Solution
Here
electric field , E = 375 V/m
Q = 55 uC
x1 = 0.02 m
x2 = 0.48 m
work done by the external force = Q * E * (x1 - x2)
work done by the external force = 55 *10^-6 * 375 * (0.02 - 0.48)
work done by the external force = -9.49 *10^-3 J
the work done by the external force is -9.49 *10^-3 J

