Example from Physics, 17.1 Understanding Diffraction and Interference

Two-Slit Interference

Suppose you pass light from a He-Ne laser through two slits separated by 0.0100 mm, and you find that the third bright line on a screen is formed at an angle of 10.95º relative to the incident beam. What is the wavelength of the light?

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Strategy
The third bright line is due to third-order constructive interference, which means that m = 3. You are given d = 0.0100 mm and $θ$ = 10.95º. The wavelength can thus be found using the equation $d \sin θ = m λ$ for constructive interference.
Solution
The equation is $d \sin θ = m λ$ . Solving for the wavelength, $λ$ , gives

$λ = \frac{d \sin θ}{m} .$
17.2

Substituting known values yields

$λ = \frac{(0.0100 mm) (\sin 10.95°)}{3} = 6.33 \times 10^{−4} mm = 633 nm .$
17.3

0 of 2 steps open

How did it go?

Strategy

Solution

Strategy

Solution