Diffraction of Light Waves

Diffraction of Light

In 1665, Grimaldi observed that the shadow cast by thin wire is much smaller than expected. Consider 2 points A and B on the same wave font A &B is also said to be 2 coherent secondary sources of light wave. You will expect the two to have an interference pattern on the screen, provided the slot is small compared to the wavelength of light. The geometrical pattern is long on the screen. Shows that they exist from a geometrical pattern of attractive dark and bright band after M&N.

Diffraction of Single Slit

Let us consider the distance image of object t produced on the screen by objective lenses of telescope which is due to diffraction. Suppose parallel phone wave front from distance object is diffracted from a rectangular slit AB (this is called Franhofer diffraction). Let light passing through AB arrive at the screen S: light source AB are said to have the same phase and are therefore coherent. Therefore the combined effect of light waves arriving at S is the algebraic sum of all the individual wave front arriving at S.