Quantum and Modern EM: X-rays, Semiconductors, Scattering

X-rays are short-wavelength, high-energy electromagnetic waves:

• Wavelength about $1\ \text{Å} = 10^{-10}$ m.
• Produced by bombarding a metal target with high-energy electrons.
• Uses: medical imaging (bone scans), cancer treatment (radiotherapy), security scanning, crystal structure study.
• NOT used for radar — radar relies on long-wavelength radio/microwaves, not short X-ray wavelengths.
• The dimensions of Planck's constant $h = E/f$ are those of angular momentum (J·s).

From $E = hf$, Planck's constant is $h = E/f$:

• Dimensionally, $[h] = \dfrac{[\text{energy}]}{[\text{frequency}]} = \dfrac{\text{J}}{\text{s}^{-1}} = \text{J}\cdot\text{s}$.
• J·s = (kg·m²/s²)·s = kg·m²/s = angular momentum (also the unit of action).
• So $h$ has the same dimensions as angular momentum, not linear momentum or torque.

Semiconductor recall facts:

• n-type: doped to have extra free electrons as the majority carriers.
• p-type: doped to have extra holes (missing electrons, behaving as positive carriers) as the majority carriers.
• A simple rectangular semiconductor wafer follows Ohm's law: its current-voltage (I-V) graph is a straight line through the origin (linear in both positive and negative quadrants).

Named scattering phenomena:

• Raman effect — when light is scattered by a molecule and its frequency CHANGES (energy exchanged with the molecule). Discovered by C. V. Raman (Nobel Prize 1930).
• Rayleigh scattering — scattering WITHOUT a frequency change (makes the sky blue).
• Do not confuse with the photoelectric effect (electron emission) or Rutherford scattering (alpha particles off nuclei).