CUET · PHYSICS · PYQ PAPER 2025

When white light consisting of wavelengths ranging from 400 nm to 700 nm passes through water (u = 4/3), then the wavelength range in water will be :

A 300 nm - 525 nm
B 500 nm - 700 nm
C 700 nm - 850 nm
D 450 Å - 750 Å

Verified Solution

Answer & Solution

Correct Answer

(A) 300 nm - 525 nm

Step-by-step Solution

Detailed explanation

\(\lambda_{water} = \frac{\lambda_{air}}{n}\) \(\lambda_{min, water} = \frac{400 \text{ nm}}{4/3} = 300 \text{ nm}\) \(\lambda_{max, water} = \frac{700 \text{ nm}}{4/3} = 525 \text{ nm}\) Wavelength range: \(300 \text{ nm} - 525 \text{ nm}\)

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.

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