Question

Two flat glass plates are separated at one end by a wire of diameter 0.20 mm; at the other end they touch. Thus, the air gap between the plates has a thickness ranging from 0 to 0.20 mm. The plates are 15.0 cm long and are illuminated from above with light of wavelength 600.0 nm. How many bright fringes are seen in the reflected light?

Answer 1

Answer:

668 bright fringes

Explanation:

t = Thickness = 0.2 mm

$\lambda$ = Wavelength = 600 nm

m = Number of fringes

We have the fringe width relation

$2t=\left(m+\frac{1}{2}\right)\lambda\\\Rightarrow m=\dfrac{2t}{\lambda}-\dfrac{1}{2}\\\Rightarrow m=\dfrac{2\times 0.2\times 10^{-3}}{600\times 10^{-9}}-\dfrac{1}{2}\\\Rightarrow m=666.166\approx 667$

So, total number of fringes will be including m = 0 is $1+667=668$