Question

Two slits separated by 1.2 mm are placed 1.40 m from a screen. Light of wavelength 480 nm and 640 nm is incident on the slits. What is the separation distance on the screen of intensity maxima of the second order?

Answer 1

Find the angles for the two wavelengths:

$$m\lambda_1=d\sin\theta_1,\\ m\lambda_2=d\sin\theta_2.\\\space\\ \theta_1=\arcsin\frac{m\lambda_1}{d}=0.046°,\\\space\\ \theta_2=\arcsin\frac{m\lambda_2}{d}=0.061°.$$

The distance between the maxima:

$$x=L(\tan\theta_2-\tan\theta_1)=0.4\text{ mm}.$$