A single slit has a width of 12.7 µm. Monochromatic light from a source passes through the slit and a fourth dark fringe (on one side of the central maximum) appears at an angle of 10.0° as measured from the CM. Calculate the wavelength of light used. What colour is this?

Question

A single slit has a width of  12.7 µm.  Monochromatic light from a source passes through the slit and a fourth dark fringe (on one side of the central maximum) appears at an angle of 10.0° as measured from the CM.  Calculate the wavelength of light used. What colour is this?

anonymous · Answer

Condition of minimum is 
$$slit\ width \times sin\  \theta = order \times wavelength$$
Put $ \theta  = 10.0^o$ , slit width = 12.7 $\mu m$  and order = 4 .

anonymous · Answer

Thanks. Got 551 nm which is green.