A very fine hair-like fiber is stuck between two microscope slides. As a result of this, there is a wedge of air between them. When the slides are illuminated normally (from above) with light of wavelength 550 nm. Bright and dark interference bands are formed. The fiber is seen to lie at the position of fifth dark band counting from the common edge. What is the diameter ( in nm) of the fiber?

Answer

`1100`

Explanation

`d=xtheta`
`x=(nlamda)/(2theta)` = condition of dark fringe
`n=0` fist dark fringe at join of plates
`n=4` fifth dark fringe at fiber
`d=xtheta=(4lambda)/2=2lambda`
`d=2xx550 nm Rightarrow 1100nm`