In November 1887, 30-year-old German physicist Heinrich Rudolf Hertz (1857–1894) presented a paper to the Berlin Academy of Sciences titled “Ueber sehr schnelle electrische Schwingungen”, published in Annalen der Physik (1887–1888).

Hertz accomplished two of the greatest experimental discoveries in physics history: generating and detecting free-space Electromagnetic (Radio) Waves (confirming Maxwell’s theory) and discovering the Photoelectric Effect.

1. Generating Electromagnetic Waves (1887–1888)

Hertz constructed an $LC$ spark gap dipole transmitter powered by an induction coil:

  • Transmitter: Discharged high-voltage sparks across a brass sphere gap, producing oscillating radio waves at $f \approx 50\,\text{MHz}$ ($\lambda \approx 6\,\text{meters}$).
  • Receiver Dipole: Placed a circular wire ring receiver with a microscopic spark gap several meters away. When the transmitter sparked, sympathetic electrical sparks jumped across the receiver gap!

Hertz proved that radio waves undergo reflection, refraction, polarization, and interference, propagating at the exact speed of light ($c = 3 \times 10^8\,\text{m/s}$):

$$\lambda f = c$$

2. Discovery of the Photoelectric Effect (1887)

While conducting spark gap experiments, Hertz noticed that the receiver spark jumped more easily when illuminated by ultraviolet light from the primary transmitter spark.

In a dedicated paper titled “Ueber den Einfluss des ultravioletten Lichtes auf die electrische Entladung”, Hertz proved that ultraviolet light ejects negative electric charges from metallic surfaces.

In 1905, Albert Einstein explained Hertz’s photoelectric effect by proposing the Light Quantum (Photon) ($E = h\nu$), winning the 1921 Nobel Prize in Physics.

Key Takeaways

  • Year: 1887
  • Key Figure: Heinrich Hertz (German Physicist)
  • Core Discoveries: Generated laboratory Radio Waves ($\text{Hertz}, \text{Hz}$) and discovered the Photoelectric Effect.
  • Maxwell Confirmed: Proved electromagnetic waves propagate at light speed ($c = \lambda f$).
  • Quantum Relevance: Discovered the photoelectric effect that led to Albert Einstein’s Photon Hypothesis ($E = h\nu$).