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Q102P

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Fundamentals Of Physics
Found in: Page 1115

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Short Answer

Monochromatic light (wavelength=450 nm ) is incident perpendicularly on a single slit (width=0.4 mm ). A screen is placed parallel to the slit plane, and on it the distance between the two minima on either side of the central maximum is 1.8mm .

(a) What is the distance from the slit to the screen? (Hint: The angle to either minimum is small enough thatsinθtanθ .)

(b) What is the distance on the screen between the first minimum and the third minimum on the same side of the central maximum?

(a) The distance of the screen from the slit is0.8 m .

(b) The distance between the first and third minima is 1.8 mm .

See the step by step solution

Step by Step Solution

Step 1: Given data

Slit width a=0.4 mm

Distance between the two minima on either side of the central maxima localid="1663048702619" y1,-1=1.8 mm

Wavelength of incident light λ=450 nm

Step 2: Definition and concept of diffraction from a grating

An optical element with a periodic structure that divides light into a number of beams that move in diverse directions is known as a diffraction grating.

The angular distance θ of the mth order minima in diffraction pattern produced from a single slit having slit width a is

asinθ=mλ …(i)

Here, λ is the wavelength of the incident light.

Step 3: (a) Determining the distance of the screen from the slit

Let the distance from the slit to the screen be D . For small angular distances

sinθtanθ=yD

Here y is the distance measured on the screen. Thus, from equation (i) the separation between the first two minima m±1 on either sides of the central maxima is

ay1,-1D=1--1λD=ay1,-12λ

Substitute the values to get

D=0.4mm×1.8mm2×450 nm=0.4×10-3m×1.8×10-3m2×450×10-9m=0.8 m

Thus, the distance is 0.8 m .

Step 4: (b) Determining the distance between the first and third minima

From equation (i), the distance between the first m=1 and third minimam=3 is

ay1,3D=3-1λy1,3=2λDa=2×450×10-9m×0.8m0.4×10-3m=1.8 mm

Thus, the distance is 1.8 mm .

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