Question

Consider a case of thin film interference as shown. Thickness of film is equal to wavelength of light in ${\mu }_2$

• A. Reflected light will be maxima if ${\mu }_1<{\mu }_2<{\mu }_3$
• B. Reflected light will be maxima if ${\mu }_1<{\mu }_2>{\mu }_3$
• C. Transmitted light will be maxima if ${\mu }_1<{\mu }_2>{\mu }_3$
• D. Transmitted light will be maxima if ${\mu }_1>{\mu }_2>{\mu }_3$

Answer 1

Answer: (A), (C)

Transmitted light will be maxima if ${\mu }_1<{\mu }_2>{\mu }_3$

$\Delta x=2{\mu }_{2}t=2\mu \left(\frac{{\lambda }_{air}}{{\mu }_2}\right)=2{\lambda }_{air}$

In option (a), two reflected rays from denser boundaries will suffer a phase difference of $\left(\pi \right)$. Hence , their mutual phase difference is zero or we can say that $\Delta x=2{\lambda }_{air}$ is the condition for maximum intensity.

Similarly, in option (c) phase difference between two transimitted rays comes out to be zero.