Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Diffraction from a Single Slit

Introduction

When a monochromatic light passes through a narrow slit, a diffraction pattern is formed on the screen placed on the other side of the slit.

Apparatus

A razor blade, laser torch

Procedure

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Make a single slit of width few hundred microns by mounting two half pieces of razor blades side by side. Fix this single slit in a vertical position. Put on laser torch and adjust so that light passes through the empty space. The direction of the laser should be perpendicular to the slit. Observe the light falling on the wall.

Discussion

You will see the diffraction fringes, very bright centre and then bright spots with gradually decreasing intensity, separated by dark spots. The number of fringes is large due to intense beam of laser torch.

Formation of alternate bright and dark fringes when a monochromatic light passes through a single slit is a strong evidence of wave nature of light.