YDSE Fringe Width and Maxima/Minima Positions – Rankers Physics

Young's Double Slit Experiment: Practice Problem & Solution

Assertion (A): In YDSE, fringes with blue light are thicker than those for red light. Reason (R): In YDSE, the \(n^{\text{th}}\) maxima always comes before the \(n^{\text{th}}\) minima.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Young's Double Slit Experiment. Understanding the underlying formula is key to arriving at the correct answer below:

Fringe width \(\beta = \frac{\lambda D}{d}\). Since \(\lambda_{\text{blue}} < \lambda_{\text{red}}\), blue fringes are thinner than red fringes, so A is false. Minima and maxima alternate, and the \(n^{\text{th}}\) dark fringe typically occurs closer to the central maximum than the \(n^{\text{th}}\) bright fringe (for (n ge 1)). So R is also false.

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