Q.

The Young's double slit interference experiment is performed using light consisting of 480 nm and 600 nm wavelengths to form interference patterns. The least number of the bright fringes of 480 nm light that are required for the first coincidence with the bright fringes formed by 600 nm light is          [2025]

1 4  
2 8  
3 6  
4 5  

Ans.

(4)

Fringe width of λ1 = 480 nm

β1=λ1Dd=480(Dd)

Similarly fringe width for λ2 = 600 nm

β2=λ2(Dd)=600(Dd)

Clearly we can see that for minimum value

5(β1)=4(β2)

That means 5th maxima of λ1 = 480 nm

coincides with 4th maxima of λ2 = 600 nm