Question

A uniform electric field of magnitude E=4.2N/C points, as illustrated in the figure below, along the negative x axis. The x and y-coordinates of points A, B, and C are shown in the figure.

a) Determine the differences in potential between points A and B, points C and B, and points C and A.

(b) What is the change in the potential electric energy of the system if a positive charge of 2nC is moved from B to C? How about from B to A?

(c) What is the change in the potential energy if a negative charge of -2nC is moved from B to C?

(d) How much work must be done to move the negative charge from B to C at constant speed?

Answer 1

a)pointa A andB are at same potential

potential between B and C=-[4.2x(-3-4) +4.2(4-4)]=29.4V

potential between A and C= 29.4V since both A and B are at same potential.

b)change in potential enrgy in moving from B to C= 2x10-9x29.4=58.8x10-9 J here potential energy decrease since change in P.E =chargexpotential

no change in going from B to A since they are at same potential

c)if a negative charge is moved then the change in potential energy=58.8x10-9 J but here potential energy increases since work is done against the field.

d)to move from B to C at constant speed work done =58.8x10-9 J