Planck’s Constant: What is it and Why Does it Matter?

Planck’s constant is one of the single most important discoveries in the history of science. If you’re familiar with Planck’s constant but can’t explain exactly what it does, then you’re in the right place. And if it’s something that you’ve never even heard of, then today we’re going to explain exactly why our world depends on it.

This article takes us deep into the spectrum of quantum mechanics, the tiny particles that make up matter, and the science that explains how everything works.

First Thing First – Classical Mechanics vs Quantum Mechanics

Before we look at Planck’s constant in more detail, let’s take a moment to quickly refresh our knowledge of classical mechanics and quantum mechanics. This will be important later on.

Classical Mechanics

Classical mechanics studies motion. It deals with the motion of bodies under the influences of various forces and the equilibrium that ensures forces are balanced. This ranges from the force you might put into kicking a football to the movements involved in rowing a boat.

In fact, the mathematical study of the motion of everyday objects is sometimes referred to as Newtonian mechanics. His first, second, and third law of motion developed many of the core principles.

Quantum Mechanics

Quantum mechanics is more abstract, focusing on the tiny particles that make up matter, and the forces involved in their interactions.

These studies conclude with some findings that many of us would consider slightly strange. Quantum mechanics is a fundamental theory that describes the physical properties of nature on a subatomic scale. It studies the behaviour of light and matter and accounts for electrons, protons, neutrons, and even quarks.

Analysing motion on such a tiny scale, many classical mechanics equations no longer hold true. Instead of existing in a specific place at a specific time, objects exist in terms of probability.

With quantum mechanics, light can, at times, behave as a particle or a photon (as opposed to a wave) and likewise, matter can behave as a wave.

Great! So Where Does Planck’s Constant Come into This?

Fantastic – hopefully we’re all on the same wavelength now (no pun intended).

Planck’s constant is a crucial part of quantum mechanics, and was developed by German physicist Max Planck. It was such an important discovery that it won him the Nobel Prize in 1918.

Planck’s constant defines the amount of energy a photon (or particle) is able to carry. It defines it according to the frequency of the wave it is travelling in. It explains how an energy transfer can only occur in a whole integer, or as a set amount, as opposed to a continuous flow: electromagnetic energy can’t flow continuously, and is instead transferred by discrete photons of light.

In his experiments, Planck had to assume that atoms could only vibrate (and therefore transfer energy) at a specific frequency – thankfully, his assumption was correct. We now know that atoms can only vibrate at a whole-number multiple of a specific frequency. That specific base frequency, given the symbol ‘h’, is Planck’s constant.

Numerically, this means that atoms can only vibrate at h, 2h, or 3h – but never at something like 2.5h, for example.

And Why Does It Matter?

Today, scientists use Planck’s constant to determine overall energy: they multiply Planck’s constant by the frequency of a wave (E=hf).

This is important – Planck’s constant effectively defines quantum mechanics. It defines how the universe permits life, in any form, to exist.

Another universal constant you may be familiar with is the speed of light. Planck’s constant is equally important: it helped develop the theory of quantum mechanics, which is crucial to human understanding of stellar evolution.

In more practical terms, Planck’s constant developed our knowledge of atoms and matter, and enabled the production of integrated circuits, transistors, and even electronic chips that all play a significant part in modern electronics technology.

Teaching Planck’s Constant

Understanding Planck’s constant isn’t easy – quantum mechanics is rarely straightforward. However, carrying out the experiments that prove Planck’s constant is relatively simple and always proves to be a popular classroom activity.

Our Planck’s Constant Apparatus functions as a ready-built circuit that’s designed to measure the photoelectric effect. When a simple graph is presented (showing amplitude against voltage), students will be able to calculate the graph’s slope and multiply it by electronic charge over the speed of light, producing Planck’s famous constant.