PHYS 1112 Module 13.2

Production of Electromagnetic Waves

Producing EM Waves with a Dipole Antenna

Electromagnetic Waves (EM waves) are waves consisting of oscillating electric and magnetic fields. These EM waves are produced by accelerating charges, like electrons speeding up, slowing down, or changing direction. Consider something called a dipole antenna – this is simply a wire that has an alternating (AC) current in it so that one end of the wire is positive and the other end is negative, like an electric dipole. As the electrons move in this dipole antenna,

• The charges are always accelerating (since the velocity is always changing)
• These accelerating charged particles emit E-fields
• These moving charged particles (current) emit B-fields
• Changing B-fields induce E-fields (Faraday’s law)
• It turns out that changing E-fields induce B-fields, too (another law we didn’t discuss – too much calculus required)

So: E-field → ΔB-field → ΔE-field → ΔB-field → ΔE-field → etc…

A changing B-field → E-field and a changing E-field → B-field →→→ Each field is a source for the other

There are no electric waves or magnetic waves, there are only electromagnetic waves.