Light from a helium-neon laser (λ = 633 nm) illuminates two slits spaced 0.50 mm apart. A viewing screen is 2.5 m behind the slits. What is the spacing between two adjacent bright fringes?

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Answer:

Explanation:

Given

wavelength [tex]\lambda =633\ nm[/tex]

distance between two slits [tex]d=0.5\ mm[/tex]

Screen is placed at a distance [tex]L=2.5\ m[/tex]

Location of a (n+1)th bright fringe is given by

[tex]x_{n+1}=\frac{L}{2d}(n+1)\lambda [/tex]

for nth bright fringe

[tex]x_n=\frac{L}{2d}(n)\lambda [/tex]

Distance between two bright fringes

[tex]x_{n+1}-x_n=\frac{L}{2d}\cdot \lambda [/tex]

[tex]x_{n+1}-x_n=\frac{2.5}{2\times 0.5\times 10^{-3}}\cdot 633\times 10^{-3}[/tex]

[tex]x_{n+1}-x_n=1.582\ mm[/tex]

Bright fringes are created from light rays.

The spacing between two adjacent bright fringes is 0.0015825m

The given parameters are:

[tex]\mathbf{\lambda = 633nm}[/tex]

[tex]\mathbf{d =0.50mm}[/tex]

[tex]\mathbf{L =2.50m}[/tex]

For a bright fringe, the location is calculated as:

[tex]\mathbf{x_{n + 1} = \frac{L}{2d}(n + 1)\lambda}[/tex]

Replace n + 1 with n

[tex]\mathbf{x_{n} = \frac{L}{2d}(n)\lambda}[/tex]

Subtract both equations

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{L}{2d}(n + 1)\lambda - \frac{L}{2d}(n)\lambda}[/tex]

Factorize

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{L}{2d}(n + 1 -n)\lambda }[/tex]

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{L}{2d}(1)\lambda }[/tex]

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{L}{2d}\lambda }[/tex]

Substitute known values

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{2.50m}{2 \times 0.50mm}(n)\times 633nm}\\[/tex]

Convert to meters

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{2.50m}{2 \times 0.50 \times 0.001m}\times 633 \times 0.000000001 m}[/tex]

[tex]\mathbf{x_{n + 1} - x_{n} = \frac{2.50m\times 633 \times 0.000000001}{0.001} }[/tex]

[tex]\mathbf{x_{n + 1} - x_{n} = 0.0015825m }[/tex]

Hence, the spacing between two adjacent bright fringes is 0.0015825m  

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