Refractive Index and Optical Density Assertion Reason

 

❓ Question

Given below are two statements:

• Assertion (A): Refractive index of glass is higher than that of air.

• Reason (R): Optical density of a medium is directly proportionate to its mass density which results in a proportionate refractive index.

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🖼️ Question Image

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✍️ Short Explanation

This problem is based on:

👉 Refractive index
👉 Optical density
👉 Assertion-Reason concept.

Main idea:

$$\boxed{ n=\frac{c}{v} }$$

Higher refractive index means light travels slower in that medium.

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🔷 Step 1 — Check Assertion (A) 💯

For air:

$$n \approx 1$$

For glass:

$$n \approx 1.5$$

Thus:

$$\boxed{ n_{glass}>n_{air} }$$

Hence Assertion (A) is correct.

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🔷 Step 2 — Check Reason (R)

Reason says:

“Optical density is directly proportional to mass density.”

This statement is NOT always true.

✔ Optical density depends on how light interacts with medium.

✔ It is not directly determined by mass density alone.

Example:

Some optically denser substances may have lower mass density.

Thus Reason (R) is incorrect.

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🔷 Step 3 — Final Conclusion

✔ Assertion (A) → Correct

✔ Reason (R) → Incorrect

Therefore:

$$\boxed{ \text{(A) is correct but (R) is not correct} }$$

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🔷 Step 4 — JEE Trap Alert 🚨

❌ Optical density ko mass density samajh lena

❌ Refractive index ko only physical density se relate kar dena

Remember:

$$\boxed{ \text{Optical density} \neq \text{Mass density} }$$

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✅ Final Answer

$$\boxed{ \text{(A) is correct but (R) is not correct} }$$

(Option 2)

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