Wave Optics II: Interference, Diffraction, Polarization
Light is a wave — and waves add, spread and can be filtered by direction
Big Idea: In Wave Optics I you saw light reflect and refract, which even a "ray" picture explains. The phenomena in this lesson — interference, diffraction and polarization — cannot be explained by rays at all. They only make sense if light is an electromagnetic wave. Two light waves can add to give brightness or cancel to give darkness; light bends around edges; and because the wave is transverse, its vibration has a direction that a filter can select. Finally, light carries momentum, so it presses on what it hits, and visible light is just a narrow band of one huge electromagnetic spectrum.
By the end you will be able to:
- state what makes two sources coherent and why it is required for a steady interference pattern;
- use the path-difference conditions for bright and dark fringes and compute fringe width in Young's experiment;
- explain diffraction and use the diffraction-grating equation d sin φ = kλ;
- describe polarization and apply Malus's law;
- estimate light pressure and place a wave on the EM spectrum scale.