Answer:
(a) 4.5° (b) 9.8 cm
Step-by-step explanation:
Given:
λ = 725*10^(-9) m
d = 18.5*10^(-3) m
L = 1.25 m
Let θ₁ be the first minimum and is equal to = λ /d
= 725*10^(-9)/18.5*10^(-6)
= 0.0392
= 0.0392
In view of smallness of this number, we have sin θ₁ = θ₁ = 0.0392
The angular width of the central maximum θm is twice the first minimum.
so θm = θ₁ = 2*0.0392 = 0.0784
The angular width in degrees is then 360*θm/2π = 4.5°. The width in centimetres is proportional to the distance to the screen (L = 125 cm) and is given approximately by θm*L = 0.0784*125 = 9.8 cm