Some of our deepest scientific insights have come from the most basic of questions. For our last lesson of the week, we will dig into the question: What is light?

The short answer to the first question (what is light?) is that light is what we experience as a narrow band of waves of specific wavelengths within the visible part of the electromagnetic spectrum. A particle of light is called a photon. Visible photons (light) have properties of both a particle and a wave. Photons travel in waves, and waves can be described mathematically by measuring wavelength, amplitude, period, frequency, and speed.

To visualize the parts of a wave, let’s bring in Bill Nye the Science Guy:

Thank’s Bill Nye! Here’s what we learned:

In the vacuum of space, nothing moves faster than light. In fact, we can say the speed of light is the cosmic speed limit. In a vacuum (like space), light travels at 300 million meters per second (3.0 x 10^{8} m/s). Because this number does not change, it is a constant and is assigned the letter c (c = speed of light). Side note: Thanks to Albert Einstein, you’ve probably heard of the equation E = mc^{2}. In words, the equation says that energy (E) is equal to mass (m) times the speed of light (c) squared. You already knew that c = speed of light!

To complete our study of the properties of light, we need to introduce Planck’s constant (h):

Next, let’s revisit the parts of a wave and make some connections:

The notes above introduce Planck’s constant, h, which has units of Joule • seconds. Planck’s constant (h) relates a photon’s energy (E) and frequency (f). Frequency is defined as the number of complete waves that pass through a point in one second. The faster a light wave is traveling (greatest speed, measured in meters per second, m/s), the higher the frequency (f, waves/second). Therefore, the faster a light wave is traveling, the higher the energy (E) of the wave. Energy has units of Joule • meters. Waves with the shortest wavelengths (λ) have the highest frequency (f) and therefore have the greatest energy (E).

If you followed all that (and I have no doubt you did!) you are ready for an introduction to Quantum Mechanics. Enjoy!