question_answer

In the case of light waves from two coherent \[{{S}_{1}}\]and\[{{S}_{2}}\] there will be constructive interference at an arbitrary point p, if the path difference \[{{S}_{1}}P\text{ }-\text{ }{{S}_{2}}P\]is

A)                  \[\left( n+\frac{1}{2} \right)\lambda \]                 

B)  \[n\lambda \]

C)                  \[\left( n-\frac{1}{2} \right)\lambda \]                  

D)  \[\frac{\lambda }{2}\]

Correct Answer: B

Solution :

                 The path difference\[{{S}_{1}}P-{{S}_{2}}P\]is a whole number of wavelength, the fringe at P is dark no bright. So, \[{{S}_{1}}P-{{S}_{2}}P=n\lambda \] (for minimum intensity)