CUET · PHYSICS · PYQ PAPER 2023

An electric dipole is placed parallel to the electric field. If W is the work done in rotating the dipole by \(30^\circ\), then work done in rotating it by \(180^\circ\) is:

A \(\frac{4}{2 + \sqrt{3}} W\)
B \(\frac{4}{2 - \sqrt{3}} W\)
C \(\frac{2}{2 + \sqrt{3}} W\)
D \(\frac{2}{2 - \sqrt{3}} W\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\frac{2}{2 - \sqrt{3}} W\)

Step-by-step Solution

Detailed explanation

\(W = pE(\cos\theta_1 - \cos\theta_2)\) \(W = pE(\cos 0^\circ - \cos 30^\circ)\) \(W = pE(1 - \frac{\sqrt{3}}{2})\) \(W_{180} = pE(\cos 0^\circ - \cos 180^\circ)\) \(W_{180} = pE(1 - (-1))\) \(W_{180} = 2pE\) \(pE = \frac{W}{1 - \frac{\sqrt{3}}{2}} = \frac{2W}{2 - \sqrt{3}}\)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Explore more questions on app

From CUET

Explore more questions on app

LIST I	LIST II
A. Transforming Principle	I. Jacob and Monod
B. Replication of DNA	II. Frederick Griffith
C. Lac operon concept	III. Alec Jeffreys
D. DNA Fingerprinting	IV. Watson and Crick