CBSE Class 12 Physics 2023: question 22

Hints

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Step-by-step solution

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1. (a) Stable equilibrium: The dipole moment $\vec{p}$ points in the same direction as $\vec{E}$, so $\theta =0^{\circ }$. In the diagram, draw the field lines pointing right and the dipole with −q on the left and +q on the right.

   ½ mark

2. Potential energy: $U=-pE\cos 0^{\circ }=-pE$, which is the minimum value.

   ½ mark

3. (b) Unstable equilibrium: The dipole moment $\vec{p}$ points opposite to $\vec{E}$, so $\theta =180^{\circ }$. In the diagram, draw the field pointing right and the dipole with +q on the left and −q on the right.

   ½ mark

4. Potential energy: $U=-pE\cos 180^{\circ }=+pE$, which is the maximum value.

   ½ mark

Answer: (a) $\vec{p}\parallel \vec{E}$, U = −pE; (b) $\vec{p}$ antiparallel to $\vec{E}$, U = +pE

Revise the chapter

• Chapter: Electric Charges and Fields (notes, formulas, where marks are lost and every past question)
• Topic: Electric Dipole