Question

The point charges -1 nC, 4 nC and 3 nC are located at (0,0,0),(0,0,1) and (1, 0,0) respectively.
The energy in the system is _____nJ.

• A. 13.36

Answer 1

The correct option is A 13.36

$W=W_1+W_2+W_3$

$=0+Q_2{V}_{21}+Q_3(V_{31}+V_{32})$

$=Q_2.\frac{Q_1}{4\pi {ϵ}_0|(0,0,1)-(0,0,0)|}+\frac{Q_3}{4\pi {ϵ}_0}[\frac{Q_2}{|(1,0,0)-(0,0,0)|}+\frac{Q_2}{|(1,0,0)-(0,0,0)|}]$

$=\frac{1}{4\pi \frac{{10}^{-9}}{36\pi }}(-4-3+\frac{12}{\sqrt{2}}){.10}^{-15}$

$W=13.36nJ$