• $summary_{type}$: concept
• $word_{count}$: 150

EM waves exhibit wave-particle duality. As waves: they show interference, diffraction, and polarization. As particles (photons): E = hf, p = $\frac{h}{lambda}$ = $\frac{E}{c}$. The wave description is adequate for radio, microwave, and most optical phenomena. The photon description is essential for photoelectric effect, Compton scattering, and atomic transitions. Intensity I = nhf (where n is photon flux per unit area per unit time). For a source of power P emitting photons of frequency f: photon emission rate = $\frac{P}{hf}$ = P*$\frac{lambda}{hc}$. Radiation pressure connects both: $P_{rad}$ = $\frac{I}{c}$ = $\frac{nhf}{c}$ = n*p (photon momentum flux). The quantization of EM radiation was Planck's revolutionary idea (1900), extended by Einstein (1905). This duality applies to all EM waves, but particle effects are more prominent at higher frequencies (higher energy per photon) and wave effects at lower frequencies.