question_answer

In Fig. two light waves of the same frequency start from the sources \[{{S}_{1}}\] and \[{{S}_{2}}\] in the same phase. The distance \[{{S}_{1}}{{S}_{2}}=\lambda /2\]. What will be the nature of the interference at the points A, B and C?

Answer:

                Both at points A and B, the path difference between the waves coming from \[{{S}_{1}}\] and \[{{S}_{2}}\] will be \[\lambda /2\].  Hence destructive interference occurs at A and B. As \[{{S}_{1}}C={{S}_{2}}C,\] the path difference between the waves reaching the point \[C\]from \[{{S}_{1}}\] and \[{{S}_{2}}\] will be zero. Hence constructive interference occurs at point C.