A plane mirror of length 30 cm is placed horizontally along with a vertical screen. A monochromatic point source of light is placed 20 cm to the left off the left edge of the mirror, at a height of 2 mm above the plane of the mirror. If the wavelength of light used is `6400Å`, then find the number of complete bright fringes formed.

Answer

`37.00`

Explanation

In `Delta S DC tan theta = ( 0.2 xx 10 ^(-2))/( 20 xx 10 ^(-2)) = 0.01`
In `Delta ABC tan theta = (y)/( 20 xx 10 ^(-2)) `
`implies y = 30 xx 10 ^(-2) xx tan theta`
`= 30 xx 10 ^(-2) xx 0.01`
= 3 mm
Fringe width,
`beta = (lamda D)/(d)= ( 6400 xx 10 ^(-10) xx 50 xx 10 ^(-2))/( 4 xx 10 ^(-3)) = 0.08 mm`
`therefore n = (y)/(beta) = (3)/(0.08) = 37.5`
So number of complete fringe will be 37.