Question

Assertion :In interference, all the fringes are of same width. Reason: In interference, fringe width is independent of the position of fringe.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

In Young's double slit experiment, position of nth order bright fringe is given by $y_n=\frac{nD\lambda }{d}$

Thus the fringe width of bright fringe =$y_{n+1}-y_n=\frac{D\lambda }{d}$ which is independent of n.

Similarly for dark fringe, position of mth order fringe is given by $y_m=(m+\frac{1}{2})\lambda \left(\frac{D}{d}\right)$

Thus the fringe width of dark fringe =$y_{m+1}-y_m=\frac{D\lambda }{d}$ which is independent of m.