Your friend has been given a laser for her birthday. Unfortunately, she did not receive a manual with it and so she doesn't know the wavelength that it emits. You help her by performing a double-slit experiment, with slits separated by 0.18 . You find that two adjacent bright fringes are 4.9 apart on a screen 1.4 mm from the slits.

Explanation:

The equation of the fringe in a double slit experiment is given by:

(1)

here:

Therefor we just need to solve the equation (1) for λ:

I hope it helps you!                              

6.3*10^-7m

Explanation:

to find the wavelength of the laser you can use the following formula:

y: height from the center of the screen to a fringe

m: order of the fringe

D: distance to the screen = 1.4m

d: distance between slits = 0.18mm

you know the separation of two fringes. Hence, you can use two consecutive fringes to find the wavelength in the following way:

hence, the walength is 6.3*10^-7m