Question

A wedge containing two glass plates touching at one end and separated at the other end by the wire of diameter $48\times {10}^{-6}m$ is illuminated normally by light of wavelength $\lambda$ = 6400 $\mathring{A}$. The length of the wedge $l$ is $12cm.$ How many bright images can be seen over this $12cm$ distance?

• A. $100$
• B. $150$
• C. $120$
• D. $90$

Answer 1

Answer: (B)

$150$

We have path difference $=2d=(2n+1)\frac{\lambda }{2}$,
where $d$ is the gap of air at any point along the length of glass plate
$⟹d=(n+\frac{1}{2})\frac{\lambda }{2}$

$⟹n\approx \frac{2d}{\lambda }=\frac{2\times 48\times {10}^{-6}}{6400\times {10}^{-10}}=150$