Question

Young's double slit experiment is carried out by using green, red and blue light, one colour at a time. The fringewidths recorded are \(W_{G}\), \(W_{R}\) and \(W_{B}\) respectively. Then

• A. \(W_{B}>W_{G}>W_{R}\)
• B. \(W_{R}>W_{B}>W_{G}\)
• C. \(W_{R}>W_{G}>W_{B}\)
• D. \(W_{G}>W_{B}>W_{R}\)

Hint:

Fringe width is directly proportional to wavelength, so order the colours by wavelength.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
In Young's double slit experiment, fringe width is \(W=\dfrac{\lambda D}{d}\).

Step 2: Dependence on Wavelength
The set-up (\(D\) and \(d\)) is the same for all colours, so \(W\propto\lambda\).

Step 3: Order of Wavelengths
Among visible colours, red has the longest wavelength, then green, then blue: \(\lambda_R\gt\lambda_G\gt\lambda_B\).

Step 4: Conclusion
Therefore \(W_R\gt W_G\gt W_B\).

Final Answer:
The fringe widths are in the order red, then green, then blue. \[ \boxed{\text{(C) }W_{R}\gt W_{G}\gt W_{B}} \]