question_answer

In Youngs double slit experiment with monochromatic light, the central fringe will be:

A)  coloured                            

B)  white

C)  bright                                  

D)  black

Correct Answer: C

Solution :

                 In Youngs double slit experiment, for maximum intensity (bright fringe) \[x=m\frac{D\lambda }{d}\] where m is path difference, D the distance between screen and coherent sources, d the distance between coherent sources and K the wavelength. Putting\[m=0,\]we get the position of the central bright fringe (which is called zero order fringe). Hence, at point 0 the path difference between two wavelets is zero. Hence, at O there is always a bright fringe. This is called the central fringe.