Diffraction and Interference Or Thomas Young was One

Diffraction and Interference Or Thomas Young was One Smart Cookie

Diffraction (Single Opening or Corner) • Definition: Bending of wave by passing it through a single opening or corner – Diffraction increases with wavelength – Diffraction decreases with aperture size • Light and sound exhibit diffraction

Huygens’ Explanation of Diffraction • Every point on every wave can be regarded as a new point source for secondary waves – Straight wave produce straight waves, curved wave produce curved waves – Straight wave passing through small opening produces curved waves (diffraction) – Could also explain refraction and reflection

Consequences of Diffraction • Radio wave propagation – AM have longer wavelength, more diffraction and greater coverage than FM – Small wavelength waves are line of site • Resolution – Resolution is how well near objects can be separated. – Diffraction increases, resolution decreases – Blue light for microscope – Electron microscope – Dolphin clicks and squeels – Q=1. 22 l/d

Thomas Young’s Experiment (More than One Opening) • Diagram of Experiment – Monochromatic and coherent light – Bright and Dark Fringes • Young’s Explanation (interference of light) • Testing Young’ explanation • Equations – D sin q = (n + 1/2)l where n= + and - 0, 1, 2, 3… for dark fringes – D sin q = nl where n=+ and - 0, 1, 2, 3, … for light fringes

Is Light a Particle or Wave? Particle Theory • Photon is massless particle of light • Photo-electric effect Wave Theory • Reflection • Refraction • Diffraction • Interference Real answer is light acts like a particle when interacting with matter and like a wave when traveling through empty space.

Interference Images • Monochromatic, coherent light • Coherent white light

From Bubbles to Holograms

Thin Film Interference (Iridescence) • Occurs when rays from top and bottom of film destructively interfere with one another. • Color is complement of color that is destroyed through interference • Color is determined by thickness of film • Examples: soap bubbles, gasoline on water, opal, CD, seashells and pearls

Diffraction Grating • Many slits instead of 2 • Reinforce bright and dark fringes in monochromatic light • Produce spectra in white light • Smaller spacing of lines produces wider spacing of bright and dark fringes • Same equations as 2 slits; d=1/slit spacing

Laser Light • • Light from incandescent source Monochromatic Light Coherent Light Laser Light Properties – Stays in straight line and does not spread out – Follows conservation of energy – All energy in one place rather than spread out

Hologram • Third dimension is recorded in interference pattern which is reproduced by irregular diffraction grating. • Set-up for making hologram • Holographic properties – Cutting results in multiple holograms – Holographic magnification