20. In a Young’s double slit experiment, if there is no initial phase difference between the light from the two slits, a point on the screen corresponding to the fifth minimum has path difference ?

20. In a Young’s double slit experiment, if there is no initial phase difference between the light from the two slits, a point on the screen corresponding to the fifth minimum has path difference ?

\( (a)\; \frac{11\lambda}{2} \)

\( (b)\; \frac{5\lambda}{2} \)

\( (c)\; \frac{10\lambda}{2} \)

\( (d)\; \frac{9\lambda}{2} \)

Answer :  \( (d)\; \frac{9\lambda}{2} \)

\( P \cdot d = (2n - 1)\dfrac{\lambda}{2} \)

\( n = 5 \)

\( P \cdot d = \dfrac{9}{2}\lambda \)