Albert Einstein is famous for revolutionizing physics with his Theory of Relativity. But did you know Einstein also discovered the science behind the solar technology now revolutionizing the way we produce energy?
In fact, Einstein was awarded his Nobel Prize, not for his famous equation E=MC2, but for the groundbreaking theory of light he developed to explain something called the Photoelectric Effect.
And the Photoelectric Effect just so happens to be the scientific process that makes it possible to turn sunshine into a cost-free, clean, and renewable source of energy.
A Mysterious Novelty
Though it literally took an Einstein to explain the science of solar power, the sun’s capacity to generate electricity was discovered by a mere teenager forty years before Albert was even born! In 1839, a 19-year-old French researcher named Edmond Becquerel exposed a conducting solution containing metal electrodes to sunlight. For some strange reason, a small electric current was produced.
Fascinating as it was, no one could explain how Becquerel’s apparatus worked and it produced too little energy to be anything more than an interesting novelty.
Scientists didn’t get a glimmer into the underlying process until almost 50 years later when, in 1887, a physicist named Heinrich Hertz discovered the Photoelectric Effect.
But Hertz’s findings turned out to be as disturbing as they were enlightening.
The Photoelectric Effect
Hertz discovered that when a metal surface is exposed to light of a high enough frequency, it emits electrons that are “knocked” free from the atoms they orbit by the light’s energy. Until Einstein came along, however, no one could make any sense of what sometimes happened when Hertz altered the experimental conditions.
The theory then accepted as settled science was that light travelled as a continuous electromagnetic wave. So, because the light’s energy was transmitted in an uninterrupted flow, even if its frequency was just a little too low to immediately break any electrons free, increasing the light’s intensity or the amount of time it struck the metal ought to yield the slight energy boost required to do the job without upping its frequency.
The problem was that neither the intensity of the light nor the length of time the metal was exposed mattered. If the light was above a certain frequency, electrons were emitted as soon as it struck the metal. But, if the frequency was even the smallest fraction too low, no matter how long you exposed the metal or how much more intense you made the light, for some reason you could never accumulate the little bit of extra energy needed to break even a single electron free.
Einstein Discovers Photons
In 1905, Einstein shattered scientific consensus by showing that Hertz’s data meant light isn’t simply a continuous wave. Instead, though it resembles a wave in certain respects, light is composed of a series of separate moving particles called photons.
When light strikes a metal surface, the energy carried by the first photon impacting an electron is either sufficient to knock it free or not. If it is, the electron is emitted from the metal surface immediately. But only one photon can impact an electron at a time. So, if the energy in that first photon is even slightly below the amount required to free the electron, hitting it with another photon won’t help unless you give it enough energy to free the electron all by itself by upping light’s frequency.
Increasing the light’s intensity just meant that more photons each with too little energy to knock the electron free would be hitting it in a given period of time. Letting the light strike the metal for a longer period of time would likewise only increase the number of insufficiently energized photons uselessly striking the electron.
Einstein showed that light was both a wave and a particle and, importantly, the complex mathematical relation between its frequency (as a wave) and the amount of energy carried by its photons (as a particle).
The precise scientific understanding Einstein gave us eventually helped engineers design the solar panels that more and more people are using every day. They maximize and efficiently channel the energy produced by the Photoelectric Effect, creating a clean, renewable, and cost-free source of energy for your home.
Next time, we’ll talk about how today’s solar panels are designed to achieve those benefits.