Max Planck: Atomic Theory & Discovery of Light

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  • 0:04 What Is Light?
  • 0:35 Who Was Max Planck?
  • 1:05 Planck's Law & Black…
  • 2:42 Photons & The Nature of Light
  • 3:24 Atomic Theory
  • 4:03 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

In 1900, a scientist named Max Planck made a discovery that would change science forever and have a profound impact on our understanding of both light and atomic structure. In this lesson, learn more about Planck's amazing discovery!

What Is Light?

What is light made of? How does it interact with objects it hits? It turns out these are very tricky questions! For hundreds of years, scientists have tried to understand light.

In the early 1900s, a German scientist named Max Planck made a big step forward in our understanding of what light is and how it works. In the process, he also advanced our understanding of atomic structure. For these remarkable discoveries, he's now recognized as one of the most influential scientists of the twentieth century. How exactly did all this happen?

Who Was Max Planck?

In 1858, Max Planck was born in the German city of Kiel where his father worked as a law professor at the University of Kiel. When he was nine years old, the family moved to Munich. After graduating from high school, Planck enrolled in the University of Munich to pursue a degree in physics. He believed that only physics would allow him to discover the true nature of the universe, and he found that idea very exciting! He graduated with a Ph.D. in Physics in 1879, and at the age of twenty-one, set out to make his mark on the world.

Planck's Law & Black Body Radiation

Planck moved to Berlin after graduation and began working as a professor of physics at the University of Berlin where he would spend the rest of his career. Even as a student, he was fascinated by energy and how it's conserved in physical processes, and he continued to study energy conservation in Berlin.

In 1900, he discovered something remarkable that would change the world of science forever. A few years earlier, another scientist working in Berlin named Gustav Kirchhoff discovered that some objects, which he called black bodies, absorbed and then emitted all the energy that hit them. He called this phenomenon black body radiation.

Planck decided to study black body radiation in more detail and found something very interesting. Black bodies always radiated an amount of energy that was proportional to the frequency of the electromagnetic waves they absorbed. He was surprised to find that energy was always emitted in tiny, discrete packets. Each tiny packet of energy is called a quantum of energy. This was the beginning of a new field of science, called quantum mechanics, that studies the nature of tiny elementary particles like protons and electrons.

This was the first time that anyone noticed energy was quantized like this, and Planck's discovery set off a revolution in physics. He showed that there was a simple relationship between the amount of energy emitted and the frequency of electomagnetic radiation. This relationship is now known as Planck's law, and the constant, h, is called Planck's constant.

As you can see from this formula appearing here, the relationship is written as:

plancks law

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