Draw a labelled diagram of Hertz's experimental set-up used to produce electromagnetic waves. Explain the generation of electromagnetic waves using this set-up.
Solution
In Hertz's apparatus two metal plates are joined to two small spheres separated by a tiny air gap and connected to the secondary of an induction coil. The coil produces a very high oscillating potential difference across the gap; this ionises the air and a spark (an oscillating discharge) jumps across, so the charges in the gap oscillate at high frequency. An accelerating/oscillating charge radiates, so these oscillating currents emit electromagnetic waves into the surrounding space. A short distance away a detector --- a wire loop with its own small spark gap --- receives the waves: the arriving EM field induces an oscillating EMF in the loop and a faint spark appears across its gap, confirming the waves.
spark-gap oscillator radiates EM waves; loop detector confirms them
