Lecture Notes: Electromagnetic Fields and Waves

Electric and Magnetic Fields

• Positive Charge & Electric Field

  • A positive charge in space creates an Electric field.
  • The Electric field radiates outward from the charge.

• Current & Magnetic Field

  • Current in a wire creates a Magnetic field.
  • The Magnetic field loops around the wire.

Creating Fields Without Charges or Currents

• Changing Electric Field & Magnetic Field Induction

  • A changing Electric field in space induces a Magnetic field, without requiring a current.

• Changing Magnetic Field & Electric Field Induction

  • A changing Magnetic field induces a changing Electric field.

James Clerk Maxwell's Realization

• Chain Reaction of Fields
  • A changing Electric field can create a changing Magnetic field, and vice versa.
  • This can create a wave that propagates independently from the originating charge or current.

Electromagnetic Waves

• Creation

  • Changing Electric or Magnetic fields can propagate as waves.
  • Antennas can oscillate charges or currents to create these waves.

• Characteristics

  • Do not require a medium (can travel through vacuum).
  • Consist of oscillating Electric and Magnetic fields perpendicular to each other and to the direction of travel.
  • Travel at the speed of light (c = 3 x 10^8 m/s).

Electromagnetic Spectrum

• Range of Wavelengths and Frequencies
  • Electromagnetic waves can have any wavelength or frequency.
  • Visible spectrum is a small part of the Electromagnetic Spectrum.

Visible Spectrum

• Wavelengths

  • Red light: ~750 nm
  • Violet light: ~400 nm

• Frequencies

  • Red light: ~4 x 10^14 Hz
  • Violet light: ~7.5 x 10^14 Hz

Beyond Visible Light

• Ultraviolet Light

  • Higher frequency than visible light, more energetic, and potentially harmful.

• X-Rays and Gamma Rays

  • Even higher frequencies and more dangerous.
  • Used in medical imaging; Gamma Rays associated with nuclear reactions.

• Infrared, Microwaves, and Radio Waves

  • Infrared: below visible red light, used in remote controls.
  • Microwaves: used in communication (cell phones, TV signals).
  • Radio Waves: lowest frequency, used in AM and FM broadcasting.

Applications and Safety

• Usefulness and Risks
  • Electromagnetic waves are essential in technology (communication, medical imaging).
  • High frequency waves (X-Rays, Gamma Rays) are dangerous due to their high energy.
  • Knowledge of the Electromagnetic Spectrum is crucial for safe and effective use of these waves.