Double Slit Lab

Physics 12- Youngs Double Slit Experiment Investigating the Wave Theory of Light Young performed his experiment, with two pinholes in a piece of paper and the sun as the light source. This experiment was very strong evidence suggesting that light was a wave. Today, we can use prepared double-slit plates of known separation and an intense monochromatic light source (laser). In this investigation, you will determine the wavelength of laser light and check your results against the known wavelength of a helium-neon laser. STEP 1- Direct the laser light through a double slit onto the screen located at least 3.0-5.0 m away (the further the better. Have your teacher confirm that you have produced an appropriate interference pattern. 1. Draw the interference pattern you observe and label the diagram with distances between nodes. Distance (L) from slits to screen: 4.08m STEP 2- Determine Δx by measuring the spacing for 4 minima on the screen. Record your measurements and determine the Average Δx . Repeat for three different slit separations First Δx (m) Second Δx (m) Third Δx ( m ) Fourth Δx ( m ) Average Δx ( m ) d(m) Slit 1 Minima spacing 0.0036 0.0073 0.0103 0.0144 0.0036 7.00 x 10 -4 m Slit 2

Minima spacing 0.0073 0.0146 0.021 0.029 0.0073 3.50 x 10 -4 m Slit 3 Minima spacing 0.0146 0.029 0.043 0.058 0.0146 1.76 x 10 -4 m 2. Determine the separation distance, d, for each slit by reading the documentation provided Slit 1: 0.7mm Slit 2: 0.35mm Slit 3: 0.176mm 3. Calculate the wavelength of the laser light for your three trials above. Show one sample calculation for the wavelength. Analysis: Bright fringes appear in a double-slit experiment when light waves from the two slits constructively interact. This occurs when the route difference, DL, is equal to a full number of wavelengths: Δx = Lλ d λ = Δxd L  λ = Δxd L Solution 2: λ = Δxd L λ = ( 7.00 × 10 − 4 m ) ( 0.0036 m ) 4.08 m λ = 6.17 × 10 − 7 m ⸫ The wavelength is 6.17 × 10 − 7 m Solution 1: λ = Δxd L λ = ( 3.50 × 10 − 4 m ) ( 0.0073 m ) 4.08 m λ = 6.26 × 10 − 7 m Statement: The wavelength of the light is 6.26 × 10 − 7 m Solution 3: λ = Δxd L λ = ( 1.76 × 10 − 4 m ) ( 0.0146 m ) 4.08 m λ = 6.29 × 10 − 7 m ⸫ The wavelength is 6.29 × 10 − 7 m