: A collimated beam of light from a helium-neon laser ( = 633) falls normally on a slit 0.5 mm wide. A lens of 50 cm focal length placed just behind the slit focuses the diffracted light on a screen located at the focal distance. Calculate the distance from the center of the diffraction pattern (central maximum) to (a) the first minimum and (b) the first secondary maximum. 2) If another collimated beam of light is added in the above diffraction experiment, the result shows that the fourth secondary maximum of this light coincides with the third secondary maximum of the helium-neon laser. What is the wavelength of this light?