An electric dipole with dipole moment 5 × 10^ -6 Cm is aligned with the direction of a uniform electric field of magnitude 4 × 10^5 ~N / C The dipole is then rotated through an angle of 60^ with respect to the electric

Correct answer: B. 1.0 J Given, aligned & p=5 × 10^ -6 Cm & E=4 × 10^5 ~N / C & θ_ i =0^ , θ_ f =60^ & Δ U=U_ f -U_ i & =-pE θ_ f -(-pE θ_ i ) & pE( θ_ i - θ_ f ) & 5 × 10^ -6 × 4 × 10^5(1-(1)/(2))=1 ~J aligned

NEET 2025

Exam: NEET
Year: 2025
Subject: Physics
Chapter: Electrostatics

NEET 2025 · Physics · Electrostatics

An electric dipole with dipole moment 5 × 10^ -6 Cm is aligned with...

An electric dipole with dipole moment

5 \times 10^{-6} \mathrm{Cm}

is aligned with the direction of a uniform electric field of magnitude

4 \times 10^5 \mathrm{~N} / \mathrm{C}

The dipole is then rotated through an angle of

60^{\circ}

with respect to the electric field. The change in the potential energy of the dipole is:

Options

A0.8 J
B1.0 J
C1.2 J
D1.5 J

Correct answer

B. 1.0 J

Step-by-step solution

Given,

\begin{aligned} & \mathrm{p}=5 \times 10^{-6} \mathrm{Cm} \\ & \mathrm{E}=4 \times 10^5 \mathrm{~N} / \mathrm{C} \\ & \theta_{\mathrm{i}}=0^{\circ}, \theta_{\mathrm{f}}=60^{\circ} \\ & \Delta \mathrm{U}=\mathrm{U}_{\mathrm{f}}-\mathrm{U}_{\mathrm{i}} \\ & =-\mathrm{pE} \cos \theta_{\mathrm{f}}-\left(-\mathrm{pE} \cos \theta_{\mathrm{i}}\right) \\ & \Rightarrow \mathrm{pE}\left(\cos \theta_{\mathrm{i}}-\cos \theta_{\mathrm{f}}\right) \\ & \Rightarrow 5 \times 10^{-6} \times 4 \times 10^5\left(1-\frac{1}{2}\right)=1 \mathrm{~J} \end{aligned}

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