1. Chapter 19: Interference & Diffraction Honors Physics Bloom High School Mr. Barry Latham

2. 19.1 Interference Incoherent light- randomly generated wave fronts ◦ Partially out of phase Coherent light- light generated in phase

3. Young’s Double-Slit Experiment Interference Fringes ◦ Coherent light shone through a barrier with 2 closely spaced, thin slits produces bright and dark bands ◦ Results from constructive and destructive interference

4. Young’s Double-Slit Experiment Interference Fringes ◦ With monochromatic light, the bands are the same color as the source, but are light and dark ◦ With white light, ROYGBIV shows up in the bands

5. Calculating Calculating x (or y)- distance from central bright spot to first maximum (m) d- distance between the slits (m) L- distance between slits and screen (m) m = x m d/L ◦ m- the location of the bright spot (unitless) ◦ 0=central spot ◦ 1=1 st spot (left and right of 0) ◦ 2= 2 nd spot (left and right of 0)

6. Practice Problem(find ) Light falls on a pair of slits 19.0  m apart and 80.0cm from a screen. The first order bright band is 1.90cm from the central bright band. What is the wavelength of light? =xd/L =(1.90x10 -2 m)(19.0x10 -6 m)/(80.0x10 -2 m) =4.51x10 -7 m = 451nm (high end of blue)

7. Practice Problem(find x) Light from a street light of wavelength 596nm is aimed at two slits that are separated by 1.9x10 -5 m. What is the distance from the central band to the first-order yellow band if the screen is 0.600m from the slits? =xd/L  x= L/d x=(596x10 -9 m)(0.600m)/(1.9x10 -5 m) x=1.88x10 -2 m = 0.0188m

8. Practice Problem(find d) In a double-slit experiment, a 632.8nm laser is used. The screen is placed 1.000m from the slits and the first-order bright band occurs 65.5mm from the central band. What is the slit separation? =xd/L  d= L/x d=(632.8x10 -9 m)(1.000m)/(65.5x10 -3 m) d=9.66x10 -6 m = 9.66  m

9. Practice Problem(find L) Light with a wavelength of 596nm passes through two slits that are separated by 0.225  m and makes an interference pattern. If the distance from the central spot to the first-order bright band is 2.00cm, how far is the screen from the slits? =xd/L  L=xd/ L=(2.00x10 -2 m)(0.225x10 -6 m)/(596x10 -9 m) L=7.55x10 -3 m = 7.55mm