A long narrow horizontal slit is positioned 1 mm above a horizontal plane mirror. The interference between the light arriving directly from the slit and the light arriving after reflection is observed on a screen located 1.0 m away from the slit. Determine the fringe-width if the wavelength of the light used is 700 nm .

Step-by-step solution

In Lloyd's mirror experiment, the interference occurs between the direct light from the slit and the reflected light from the mirror. The virtual image of the slit formed by the mirror acts as the second coherent source. The distance between the real slit and its virtual image is the effective slit separation d . d = 2h = 2 1 mm = 2 mm = 2 10⁻³ m The distance to the screen is D = 1.0 m and the wavelength of light is = 700 nm = 700 10⁻⁹ m . The fringe-width is given by the formula: = D d Substituting the values: = 7