Four identical charges 15 C each are brought from infinity a

Four identical charges (+1.5 C each) are brought from infinity and fixed to a straight line. Each charge is 0.36 m from the next. Determine the electric potential energy of this group.

Solution

For this problem use the formula:

U = k[(q1q2 / r12) + (q1q3 / r13) + (q1q4 / r14) + (q2q3 / r23) + (q2q4 / r24) + (q3q4 / r34)]

Here we go...

U = (8.99 x 10^9 Nm²/C²) x [ ((1.5 C x 1.5 C) / 0.36 m) + ((1.5 C x 1.5 C) / 0.72 m) + ((1.5 C x 1.5 C) /1.08 m) + ((1.5 C x 1.5 C) / 0.36 m) + ((1.5 C x 1.5 C) / 0.72 m) + ((1.5 C x 1.5 C) / 0.36 m) ]

= 0.24 J/C