NEET · Physics · STD 12 - 2. Electric potential and capacitance
An electric dipole with dipole moment \(5 \times 10^{-6} Cm\) is aligned with the direction of a uniform electric field of magnitude \(4 \times 10^5 N / C\) 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:
- A 0.8 J
- B 1.0 J
- C 1.2 J
- D 1.5 J
Answer & Solution
Correct Answer
(B) 1.0 J
Step-by-step Solution
Detailed explanation
Given,
\(p =5 \times 10^{-6} Cm \)
\( E =4 \times 10^5 N / C \)
\( \theta_{ i }=0^{\circ}, \theta_{ f }=60^{\circ} \)
\( \Delta U = U _{ f }- U _{ i } \)
\( =- pE \cos \theta_{ f }-\left(- pE \cos \theta_{ i }\right) \)
\( \Rightarrow pE \left(\cos \theta_{ i }-\cos \theta_{ f }\right) \)
\( \Rightarrow 5 \times 10^{-6} \times 4 \times 10^5\left(1-\frac{1}{2}\right)=1 J\)
\(p =5 \times 10^{-6} Cm \)
\( E =4 \times 10^5 N / C \)
\( \theta_{ i }=0^{\circ}, \theta_{ f }=60^{\circ} \)
\( \Delta U = U _{ f }- U _{ i } \)
\( =- pE \cos \theta_{ f }-\left(- pE \cos \theta_{ i }\right) \)
\( \Rightarrow pE \left(\cos \theta_{ i }-\cos \theta_{ f }\right) \)
\( \Rightarrow 5 \times 10^{-6} \times 4 \times 10^5\left(1-\frac{1}{2}\right)=1 J\)
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