Electrostatics 4 Question 3
3. An electric field of $1000 V / m$ is applied to an electric dipole at angle of $45^{\circ}$. The value of electric dipole moment is $10^{-29}$ $C-m$. What is the potential energy of the electric dipole?
(a) $-9 \times 10^{-20} J$
(b) $-10 \times 10^{-29} J$
(c) $-20 \times 10^{-18} J$
(d) $-7 \times 10^{-27} J$
(Main 2019, 11 Jan II)
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Solution:
- Given,
$$ \begin{aligned} & \mathbf{E}=1000 V / m \\ & \theta=45^{\circ} \\ & \mathbf{p}=10^{-29} C-m \end{aligned} $$
and
We know that, electric potential energy stored in an electric dipole kept in uniform electric field is given by the relation
$$ \begin{aligned} U & =-\mathbf{p} \cdot \mathbf{E}=-P E \cos \theta \\ & =-10^{-29} \times 1000 \times \cos 45^{\circ} \\ \Rightarrow \quad U & \approx-7 \times 10^{-27} J \end{aligned} $$
