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  • (a) Find the expression for the potential energy of a system of two point charges and located at

(a) Find the expression for the potential energy of a system of two point charges q_{1} and q_{2} located at \vec{r_{1}} and \vec{r_{2}}. respectively in an external electric field \vec{E}.

(b) Draw equipotential surfaces due to an isolated point charge (-q) and depict the electric field lines.

(c) Three point charges 1\mu C,\ -1\mu Cand 2\mu C are initially infinite distance apart. Calculate the work done in assembling these charges at the vertices of an equilateral triangle of side 10 cm.

 

 
 
 
 
 

Answers (1)

Work done in bringing q_1 from infinity against the electric field

w=q_1V|\vec{r_1}|

Work done in bringing q_2 from infinity against the electric field

w=q_2V|\vec{r_2}|

Work done on q_2 against the field due to q_1

=\frac{q_1q_2}{4\pi\epsilon_0r_{12}}

The potential energy of the system= Total work done in assembling the
system

=q_1V|\vec{r_1}|+q_2V|\vec{r_2}|+\frac{q_1q_2}{4\pi\epsilon_0r_{12}}.

b)

c)

Work done= charge in potential energy

\\=[k\frac{q_1q_2}{r_{12}}+k\frac{q_1q_3}{r_{13}}+k\frac{q_2q_3}{r_{13}}]\\\\=\frac{9\times10^{-3}}{0.1}(-1-2+2)\\\\=-9\times10^{-2}J

Posted by

Safeer PP

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