What is the electric potential energy of the group of charges in (Figure 1)? Assume that q = -3.5 nC.

In general when there is a system of N charges then to calculate the electric potential energy of the system, we need to sum the energies of each pair of charges formed (not repeated)

Q = 3.0 nC

q = -2.0 nC

Let r1 = 3.0 cm

r2 = 4.0 cm

then, r3 = 5.0 cm

Now the potential energy of the system would be:

£ bo .

U = 9*10^{9}*3.0*10^{-9}* \frac{10^{-9}}{10^{-2}}*(\frac{-2}{3.0} + \frac{-2}{4.0} + \frac{3}{5.0})

U = -1.53 *10^{-6} \ J is the required answer

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