Key Terms
Wave optics (physical optics)
The branch of optics dealing with light behavior when it exhibits wave characteristics, especially when interacting with
Equation in vacuum
C = f * lambda
Visible range
Approximately 380 nm to 760 nm.
Coherent
Waves are in phase or have a definite phase relationship.
Incoherent
Waves have random phase relationships.
Applies to
All wave types (water, sound, light, matter waves).
Diffraction
The bending of a wave around the edges of an opening or obstacle.
Why light casts sharp shadows through a doorway
Light wavelength (~500 nm) is far smaller than the door (~1 m); it acts like a ray. Sound at 1000 Hz has lambda ~0.34 m,
Setup
Single source -> single slit (to create coherence) -> double slit -> screen. Result: alternating bright and dark interfe
Iridescence in butterfly wings and bird feathers
Structural color from regular reflecting rows acting as gratings. CDs, opals: same principle.
DESTRUCTIVE INTERFERENCE (minima) - SINGLE SLIT
W * sin(theta) = m * lambda, where m = 1, 2, 3, ... (m NOT equal to 0)
EXAMPLE VALUES
Lambda = 550 nm, second minimum at 45 degrees -> W = m * lambda / sin(theta) = 2 * 550 nm / sin(45 deg) = 1555 nm = 1.56
If objects are at distance s from the aperture
Minimum separation = s * theta_min = 1.22 * s * lambda / D
Resolving power of a microscope
D_min = lambda / (2 * NA), or equivalently d_min = lambda * s / (1.22 * D) from the Rayleigh form.
To reduce spreading
Increase D. This is why laser beams sent to the Moon are expanded through a telescope first.