Asingle slit diffraction experiment performed with an argon laser of wavelength 454.6 nm produces a pattern on a screen with dark fringes (minima) separated by 10 mm. if we switch to a helium laser of wavelength 632.8 nm, without changing anything else in the setup, what will be the new separation between dark fringes? select one:

a. 7.2 mm

b. 6.1 mm

c. 13.9 mm

d. 17.3 mm

e. 15.2 mm

To develop this problem it is necessary to apply the concepts related to Interference and the Two slit experiment.

Young's equation defines the separation between fringes this phenomenon as,

Where,

Wavelength

d = Separation between fringes

a =  Slit width

D = Distance between the slits and screen

Then for the two case we have

Calculating the new separation between the fringes would be

We have then,

Therefore the correct answer is c.