In YDSE performed with wavelength `lambda = 5890 Å` the angular fringe width is `0.40^(@)`. What is the angular fringe width if the entire set-up is immersed in water?

Explanation

Angular fringe width is given by
`beta theta = (lambda)/(d)`
`beta_(theta)^("air") = (lambda_("air"))/(d) , beta_(theta)^("water") = (lambda_("water"))/(d)`
`(beta_(theta)^("air"))/(beta_(theta)^("water")) = (lambda_("air"))/(lambda_("water")) = (n_("air"))/(n_("water")) = (3)/(4)`
`:. beta_(theta)^("water") = (3)/(4) beta_(theta)^(beta) = 0.40^(@) xx (3)/(4) = 0.30^(@)`