Solved Insights for JEE Main 2025 Physics Question 22 Jan Shift 1 | Assertion-Reason Question from 22 Jan Shift 1 with Solution
This question appeared in the JEE Main 2025 Physics Question 22 Jan Shift 1 paper held on 22nd January (Shift 1). It’s based on the topic Young’s Double Slit Experiment and tests your understanding of how light behaves in optically denser media.
❓ Question:
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): If Young’s double slit experiment is performed in an optically denser medium than air, then the consecutive fringes come closer.
Reason (R): The speed of light reduces in an optically denser medium than air while its frequency does not change.
In the light of the above statements, choose the correct option:
- (A) Both A and R are true, and R is the correct explanation of A
- (B) Both A and R are true, but R is not the correct explanation of A
- (C) A is true, but R is false
- (D) A is false, but R is true
✅ Correct Answer: (A)
🧠 Explanation:
In Young’s Double Slit Experiment (YDSE), the fringe width β is given by:
β = λD / d
- Where λ is the wavelength in the medium
- D is the distance between the screen and the slits
- d is the separation between the slits
When the experiment is performed in an optically denser medium (like water or glass), the speed of light decreases, and since frequency remains constant, the wavelength also decreases.
This causes the fringe width to reduce, making the fringes come closer together.
So, both statements are correct and the Reason (R) correctly explains Assertion (A).
See the Video Solution here
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