A plane mirror of length 30 cm is placed horizontally along with a vertical screen. A monochromatic point source of light is placed 20 cm to the left off the left edge of the mirror, at a height of 2 mm above the plane of the mirror. If the wavelength of light used is 6400 A ∘ , then find the number of complete bright fringes formed.

Question

A plane mirror of length 30 cm is placed horizontally along with a vertical screen. A monochromatic point source of light is placed 20 cm to the left off the left edge of the mirror, at a height of 2 mm above the plane of the mirror. If the wavelength of light used is 6400 A ∘ , then find the number of complete bright fringes formed.,

MARKS App · Accepted Answer

y = 3 0 cm tan θ = 3 0 cm 0.2 2 0 = 0.3 cm = 3 mm = λ D d = 6 4 0 0 × 1 0 - 1 0 × 0.5 4 × 1 0 - 3 = 8 0 0 × 1 0 - 7 = 0.08 mm n = y w = 3 0.08 = 3 0 0 8 = 7 5 2 = 37.5 So no. of complete fringe will be 37. (take a note first bright fringe will be at a distance of w 2 above edge)

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