Question

White light is normally incidents on a soap film. The thickness of the film is $0.5\mu m$ and its refractive index is $1.33$. Which wave length will be reflected maximum in the visible region?

• A. $26600A^o$
• B. $8860A^o$
• C. $5320A^o$
• D. $3800A^o$

Answer 1

The correct option is C $5320A^o$

Given : $n=1.33$, $d=5\times {10}^{-7}$ m

For maximum reflection, $2nd=(m+\frac{1}{2}){\lambda }_m$

$\therefore$ $2\left(1.33\right)(5\times {10}^{-7})=(m+\frac{1}{2}){\lambda }_m$ $⟹{\lambda }_m=\frac{26600}{2m+1}$ $A^o$

Thus ${\lambda }_o=26600$ $A^o$, ${\lambda }_1=8866.67$ $A^o$, ${\lambda }_2=5320$ $A^o$

Hence,$5320$ $A^o$ will be reflected maximum in the visible region.