Question

Young’s double slit experiment is carried with two thin sheets of thickness $10.4\mu m$ each and refractive index ${\mu }_1=1.52$ and ${\mu }_2=1.40$ covering the slits $S_1$ and $S_2$, respectively, If white light of range 400 nm to 780 nm is used, then which wavelength will form maxima exactly at point O, the centre of the screen?

• A. 416 nm only
• B. 624 nm only
• C. Both 416 nm and 624 nm
• D. None of these

Answer 1

The correct option is C Both 416 nm and 624 nm

Path difference = $({\mu }_1-{\mu }_2)t=12480\dot{A}$
For maxima, $n\lambda =12480\dot{A}$
${\lambda }_1=12480\dot{A}$, ${\lambda }_2=6240\dot{A}$
${\lambda }_3=4160\dot{A}$, ${\lambda }_4=3120\dot{A}$
Therefore, both $6240\dot{A}$ and $4160\dot{A}$ exist in the spectrum.