Question

there exists a uniform electric field E = 4 * 10 ^5 V/m directed along negative x axis such that electric field at origin is zero . A charge of -200 microcoloumb is placed at origin and a charge of 200 microcoloumbis placed at ( 3m , 0) , what is the electrostatic potential energy of the system ?

Answer 1

Dipole moment of the two charges is

p = q × l

p = 200×10^-4 × 3

p = 1.2×10^-3

P.E. = pEcos∅

P.E. = 1.2×10^-3 × 4×10^5 [ cos∅ = 0°]

P.E. = 4.8×10^2 J

Please confirm the answer I'm not sure about it...

Answer 2

Answer: The correct answer is $-(12\times 10^{7) J}$.

Explanation:

The expression for the electrostatic potential energy of the system is as follows;

$U= k\frac{q_{1}q_{1}}{r}$

Here, k is the constant, ${q_{1}, q_{1}}$ are the charges and r is the distance.

In the given problem,  a charge of -200 mC is placed at origin and a charge of 200 mc is placed at ( 3 m , 0).

Put $k= 9\times 10^{9} Nm^{2}C^{-2}$, ${q_{1}=-200 microcoloumb, q_{1}=-200 microcoloumb}$ and r = 3m.

$U= (9\times 10^{9})\frac{(-200 mC)(200 mC)}{3}$

$U=- (12\times 10^{7) J}$

Therefore, the electrostatic potential energy is $-(12\times 10^{7) J}$.