Question:medium

In Young's double slit experiment, if the source of light changes from orange to blue, then

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Smaller wavelength → smaller fringe width → fringes get closer.
Updated On: Apr 17, 2026
  • the central bright fringe will become a dark fringe
  • the distance between consecutive fringes will decrease
  • the distance between consecutive fringes will increase
  • the intensity of the minima will increase.
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The Correct Option is B

Solution and Explanation

Step 1: Understanding the Concept:
The distance between consecutive fringes is known as the fringe width (\(\beta\)). It depends on the wavelength of the light used in the experiment.
Step 2: Key Formula or Approach:
The fringe width \(\beta\) is given by:
\[ \beta = \frac{\lambda D}{d} \]
Where \(\lambda\) is the wavelength, \(D\) is the distance between slits and screen, and \(d\) is the distance between the two slits.
Step 3: Detailed Explanation:
In the visible light spectrum, wavelengths follow the VIBGYOR order.
Wavelength of Blue light (\(\lambda_{B}\)) is less than the wavelength of Orange light (\(\lambda_{O}\)):
\[ \lambda_{B}<\lambda_{O} \]
Since the geometry of the experiment (\(D\) and \(d\)) remains constant:
\[ \beta \propto \lambda \]
When we switch from orange light to blue light, the wavelength decreases. Consequently, the fringe width \(\beta\) also decreases.
The central bright fringe remains bright because the path difference at the center is zero for all wavelengths.
Step 4: Final Answer:
The distance between consecutive fringes will decrease.
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