Chapter 46: Problem 1

Question: When monochromatic light is incident on a slit $a~=~0.022~{\rm mm}$ wide, the first diffraction minimum is observed at an angle of $\theta_1~=~1.8^o$ from the direction of the incident beam. Find the wavelength of the incident light.

Solution: We know that the first minimum is located at an angle such that $a\sin\theta_1~=~\lambda$. Inserting the appropriate numbers gives

$$\lambda~=~2.2\times 10^{-5}\sin\left( {1.8\pi\over 180}\right)~=~690~{\rm nm} \ \ \ .$$