A point is situated at 6.5 cm and 6.65 cm from two coherent sources. Find the nature of illumination at the point if wavelength of light is 5000 Å.

Explanation

Given : ` S _ 1 P = 6.50 cm, S _ 2 P = 6.65 cm , lamda = 5000 Å `
Path difference = ` n lamda `
` S _ 2 P - S _ 1 P = n lamda `
` therefore " " n = ( S _ 2 P - S _ 1 P ) /( lamda ) `
` = ( ( 6.65 - 6.50 ) xx xx 10 ^( - 2 ) ) / ( 5 xx 10 ^( - 7) ) `
` = 0.00 3 xx 10 ^( 5 ) = 3000 `
` therefore ` Path difference = ` 3000 lamda `
As the path difference is an integral multiple of wavelength, point appear bright.