What is the angle between the first-order and second-order bright fringes for a yellow light with a wavelength of 605 nm, and a distance between two slits of 0.0550 mm?

In order to get the answer, use the formula nλ = dsin (θ) where λ is the angle and the wavelength. Work out λ for n = 1 and take away from n = 2 as it is asked to find the difference. Then take the tetha in radians as it allows to use the small angle approximation whereas long as θ is small. So Sin (θ) is approximate θ. For n = 1, θ = λ/d = 0.011 and n = 2, λ/d = 0.022. The difference being 0.011 radians which is 0.630 degrees.