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Physics · Wave Optics

JEE Main 2025 — 22 January, Morning Shift — Question 48

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 most appropriate answer from the options given below :

  1. Option A:

    Both (A) and (R) are true and (R) is the correct explanation of (A)

    Correct
  2. Option B:

    (A) is false but (R) is true.

  3. Option C:

    Both (A) and (R) are true but ( R\mathbf{R} ) is not the correct explanation of (A)

  4. Option D:

    (A) is true but ( RR ) is false.

Answer: A

Step-by-step solution

β(\beta( fringe width )=λDd)=\frac{\lambda D}{d}

In denser medium,

λ↓⇒β↓\lambda \downarrow \Rightarrow \beta \downarrow

⇒\Rightarrow fringe come closer Also,

μ=CV⇒V=Cμ\mu=\frac{\mathrm{C}}{\mathrm{V}} \Rightarrow \mathrm{V}=\frac{\mathrm{C}}{\mu}

Frequency remains same, ⇒μ=λvac. fλmed f⇒λmed =λvac. μ\Rightarrow \mu=\frac{\lambda_{\text {vac. }} \mathrm{f}}{\lambda_{\text {med }} \mathrm{f}} \Rightarrow \lambda_{\text {med }}=\frac{\lambda_{\text {vac. }}}{\mu}

Answer key and solution verified before publishing.

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Exam
JEE Main 2025
Paper
22 January, Morning Shift
Subject
Physics
Chapter
Wave Optics
Topic
Young's Double Slit Experiment and Its Modifications
Given below are two statements: one is labelled as Assertion (A) and… | JEE Main 2025 PYQ with Solution · DhiX AI