Question

Light from a helium- neon laser ( λ = 633 nm) passes through a narrow slit and is seen on a screen 2.0 m behind the slit. The first minimum of the diffraction pattern is observed to be located 1.2 cm from the central maximum. How wide is the slit?

Answer 1

Wave length ,λ = 633 nm=633*10^-9 m

Distance of the slit from screen,L= 2 m

Pattern location,y1=1.2 cm =0.012 m

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Angle,θ1 =y1/L

            =0.012/2

            =  0.006 rad

Calculate the width of slit:

a= λ/sinθ1

   ≈λ/θ1

   =633*10^-9/0.006

   =0.0001055 m

   =0.1055 mm