30 DIFFRACTION

30 Diffraction

This chapter continues exploring wave behavior under the modified title of "Diffraction" rather than "Interference".
There is no distinct physical difference between interference and diffraction; the terms are used based on the number of sources involved:
- Few sources (e.g. two): usually termed interference.
- Many sources: commonly referred to as diffraction.
Discussion focuses on adding contributions from n equally spaced oscillators (all equal amplitude but differing phases).

A diffraction grating consists of multiple closely spaced slits (or scratched surfaces) that diffract light into various angles, allowing for spectral analysis based on interference.

The resolving power refers to the ability of a grating to distinguish between two wavelengths. Defined by the Rayleigh criterion, it describes the separation necessary to perceive two distinct wavelengths as separate.
- ( rac{\Delta \lambda}{\lambda} = \frac{1}{mn} ) where ( m ) is the order of the maximum, and ( n ) is the number of lines per unit length.

Explores the design of radio telescopes using arrays of dipole antennas to determine the directional position of radio sources in the sky.
- The resolving angle ( \theta = \frac{\lambda}{L} ), where ( L ) is the antenna array length.

Discusses interference effects observed in thin films and other conditions giving rise to colored reflections, based on constructive and destructive interference.

Examines how light interacts with opaque objects, producing diffraction patterns characterized by oscillations and rapid intensity variations near the shadows cast by these objects.

Derives the electric field due to a plane of oscillating charges and identifies the distance dependence relevant for far-field observations.
The field at a distant point is approximately proportional to the velocity of the charges, factoring in time delay due to propagation speed.