KCET · Physics · Ray Optics

A monochromatic beam of light is travelling from medium \(A\) of refractive index \(n_{1}\) to a medium \(\mathrm{B}\) of refractive index \(\mathrm{n}_{2}\). In the medium \(A\), there are \(x\) number of waves in certain distance. In the medium B, there are \(y\) number of waves in the same distance. Then, refractive index of medium \(A\) with respect to medium \(B\) is

A \(\frac{x}{y}\)
B \(\frac{y}{x}\)
C \(\sqrt{\frac{x}{y}}\)
D \(\frac{x}{y-x}\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(\frac{x}{y}\)

Step-by-step Solution

Detailed explanation

If \(x\) number of waves of wavelength \(\lambda_{1}\) and \(y\) number of waves of wavelength \(\lambda_{2}\) are present in same distance s, then
\(\mathrm{s}=\mathrm{x} \lambda_{1}=\mathrm{y} \lambda_{2} \)
\(\text {or } \frac{\mathrm{x}}{\mathrm{y}}=\frac{\lambda_{2}}{\lambda_{1}}=\frac{\mathrm{n}_{1}}{\mathrm{n}_{2}} \)
\(\therefore \frac{\mathrm{n}_{1}}{\mathrm{n}_{2}}=\frac{\mathrm{x}}{\mathrm{y}}\)

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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