Einstein’s Law of the Photoelectric Effect: A Closer Look

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The photoelectric effect relates to wave-particle duality and quantum mechanics. It involves photoelectrons, or electrons that are emitted when a surface absorbs energy from light.

The Photoelectric Effect at Work

The way the photoelectric effect works is quite simple: when light shines onto a metal surface, that surface emits electrons. For instance, simply shining Ultra Violet light onto a metal sheet or a metal dish could create a circuit.

This happens because light is made up of electromagnetic waves, and these waves carry energy. Thus, if light hits an electron on a metal sheet or metal dish, enough energy may be transferred to knock the electron out of its original atom.

This is not true for all beams of light, however. Per Boston University, the beam has to be above a certain energy threshold: if light below the threshold frequency is used, it won’t emit electrons. If light above the threshold frequency is used, it will always cause electrons to be emitted, even if the light is not intense. This is because a certain amount of energy is required to eject an electron from its original surface.

The photoelectric effect works when the electrons of a surface interact with the photons (packets of energy) that light consists of. While photons have no mass, they do contain momentum and energy. If the photons merging with electrons create more energy than the work function (the energy binding an electron to its original atom), the electron is ejected.

The Photoelectric Effect on Non-Metals

The Argonne National Laboratory says that the photoelectric effect is usually discussed only in regards to metal surfaces. In principle, it may be able to work on non-metal surfaces, but in practice, this isn’t likely. The reason for this is that only metals have spare electrons in their outer shells: these spares are emitted when light shines upon metal.

Another reason the photoelectric effect isn’t likely to work on non-metals is that the energy needed to remove an electron form a non-conducting surface is much greater than the energy required to remove an electron from a conductor.

Heinrich Hertz’s Role in the Photoelectric Effect

Heinrich Hertz was a German physicist known for being the first to broadcast and receive radio waves. He began studying electromagnetic theory in 1883 and established with certainty that light and heat are electromagnetic radiations.

In 1887, Hertz helped discover the photoelectric effect. This discovery occurred when he noticed that a charged object loses its charge faster when it is illuminated by ultraviolet light. Hertz never explained why this phenomenon occurred, however, allowing Albert Einstein to take over where he left off.

Albert Einstein’s Role in the Photoelectric Effect

Albert Einstein was born in Germany in 1879. In 1905 — widely regarded as Einstein’s “Miracle Year” — he submitted four papers to the Annalen der Physik, a highly respected physics journal. These four papers discussed the Brownian motion, special relativity (which is part of the theory of relativity), the equivalence of matter and energy, and the photoelectric effect. In regards to the latter, he was the first to explain why the phenomenon worked.

In 1921, Einstein received the Nobel Prize for Physics. While it was stated that he won the prize for his work regarding the photoelectric effect, some believe he was really awarded the prize for his theory of relativity. However, this theory — which suggested that movement is relative to the observer — was highly controversial at the time.

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