Two coherent fight sources A and B with separation `2lambda` are placed on the x-axis symme-trically about the origion. They emit light of wavelength `lambda`. Obtain the positions of maxima on a circle of large radius, lying in the x-y plane and with centre at the origion.

Explanation

For P to have maximum intensity, d cos `theta =n lamda`
`2 lamda cos theta = n lamda rArr cos theta =n/2 ` where n is integer
For `n = 0, theta = 90^@ , 270^@`
`n= pm 1, theta =60^@ , 120^@ , 240^@, 300^2`
`n = pm2, theta =0^@ , 180^@`
So, positions of maxima are at
`theta = 0^@ , 60^@ , 90^@ , 120^@ , 180^@, 240^@, 270^@` and `300^@` i.e., 8 positions will be obtained .