Determine the wavelength of a monochromatic beam of light that impinges on a double slit with a slit separation of 2.80 mm. bright fringes are produced on a screen 1.20 m from the double slit. the brights are separated by .024m.

Explanation:

For constructive interference, the expression is:

Where, m = 1, 2, .....

d is the distance between the slits.

The formula can be written as:

....1

The location of the bright fringe is determined by :

Where, L is the distance between the slit and the screen.

For small angle ,

So,  

Formula becomes:

Using 1, we get:

For two fringes:

The formula is:

For first and second bright fringe,  

Given that:

d = 2.80 mm

L = 1.20 m  

Also,  

1 mm = 10⁻³ m

d = 2.80×10⁻³ m

Applying in the formula,