Electromagnetic waves are fascinating phenomena that carry energy through space. They're created when electric charges oscillate, producing intertwined electric and magnetic fields that propagate at the speed of light.

These waves are the foundation of modern communication technologies like radio and TV. Understanding their production and propagation is key to grasping how information travels wirelessly across vast distances in our interconnected world.

Electromagnetic Wave Production and Propagation

Propagation of electromagnetic waves

• AC generator produces alternating current and voltage
  • Charges oscillate back and forth in the generator's coils (electrons in copper wire)
• Oscillating charges create time-varying electric and magnetic fields
  • Electric field produced by changing distribution of charges (voltage)
  • Magnetic field produced by motion of charges or current (amperage)
• Electric and magnetic fields are perpendicular to each other and to direction of wave propagation
  • Propagation direction is outward from the AC generator (radio tower antenna)
• Fields regenerate each other as they propagate through space
  • Changing electric field creates a changing magnetic field (Faraday's law)
  • Changing magnetic field creates a changing electric field (Ampère's law)
  • Self-sustaining cycle allows waves to travel long distances (radio, TV signals)
• Electromagnetic waves propagate at speed of light $c \approx 3 \times 10^8 \text{ m/s}$ in vacuum
  • Speed is slightly slower in air or other media (glass, water)
• This process of wave generation and propagation is described by Maxwell's equations

Relationship of field strengths

• Electric field strength $E$ and magnetic field strength $B$ are proportional to each other
  • As $E$ increases, $B$ increases proportionally and vice versa
• Ratio of $E$ to $B$ is equal to speed of light $c$ in vacuum: $E/B = c$
  • Ratio is a constant regardless of wave frequency or amplitude
• In SI units, $E$ measured in volts per meter (V/m) and $B$ measured in teslas (T)
  • $1 \text{ T} = 1 \text{ N} / (\text{A} \cdot \text{m})$
  • Tesla is a large unit, so $\mu$T (microtesla) and nT (nanotesla) often used
• Direction of $E$ and $B$ fields are perpendicular to each other and to propagation direction
  • $E$, $B$, and propagation direction form a right-handed triad
  • Point thumb in $E$ direction, fingers in $B$ direction, palm faces propagation direction

Calculation of peak magnetic field

• Relationship between peak electric field strength $E_0$ and peak magnetic field strength $B_0$:
  • $E_0 / B_0 = c$
  • Peak values occur at the same points in the wave cycle
• Rearrange equation to solve for $B_0$:
  • $B_0 = E_0 / c$
• Example calculations:
  1. If $E_0 = 1000 \text{ V/m}$, then $B_0 = (1000 \text{ V/m}) / (3 \times 10^8 \text{ m/s}) \approx 3.33 \times 10^{-6} \text{ T} = 3.33 \text{ }\mu\text{T}$
  2. If $E_0 = 250 \text{ mV/m}$, then $B_0 = (0.25 \text{ V/m}) / (3 \times 10^8 \text{ m/s}) \approx 8.33 \times 10^{-10} \text{ T} = 0.833 \text{ nT}$

Electromagnetic Waves and Radiation

• Electromagnetic waves are a form of radiation that can transfer energy through space
• The electromagnetic spectrum encompasses all types of electromagnetic radiation
• Electromagnetic waves exhibit wave-particle duality, behaving as both waves and particles (photons)
• Antennas are devices used to transmit or receive electromagnetic waves