Goal: To understand electromagnetic waves. Objectives: 1) to learn that the term electromagnetic wave is scarier sounding than it actually is 2) to understand how accelerating charges emit light 3) To learn about the electromagnetic spectrum 4) To understand the speed of light

Electromagnetic waves Are just a fancy way of saying light waves. However, this “light” isn’t just the light that we can see. It turns out that light comes in a lot of forms.

Properties of light Light can act like either a particle or a wave. Most commonly acts like a wave. Like waves you are familiar with, light waves have a wavelength and energy. Energy ~ speed of light / wavelength

Which of the following would emit light waves? Dentist X-ray machine An outgoing radio tower Radar machine The Earth Neon sign All of the above None of these

Spectrum of Electromagnetic Radiation RegionWavelength (Angstroms) Wavelength (centimeters) Frequency (Hz) Energy (eV) Radio> 10 9 > 10< 3 x 10 9 < Microwave x x Infrared x x x Visible x x x x Ultraviolet x x x X-Rays x x Gamma Rays< 0.1< > 3 x > 10 5

Uses Different forms of light have different amounts of energy. This allows us to do different things. For example, higher energy light waves go further into our bodies. Thus the use for X-rays. Also, different substances reflect and absorb light differently. Lasers…

How is light created? Light is created by charges changing energy states – to conserve energy. Most comes from an atom. Later in the course we will look at atoms. When a charge changes directions, it changes energy. But energy is conserved! So, the particle will emit a PHOTON of light. Photon is a single wave of light.

The speed of light As we will learn later the speed of light cannot be broken directly. In a vacuum the speed of light (denoted as c) is: c = 1 / (ε 0 μ 0 ) 1/2 = 3 * 10 8 m/s OR: c = 1 light year / year (1 light year being the distance light travels in a year, and 1 light year = 6 trillion miles)

Conclusion We learn that light is a wave that can sometimes act like a particle. We learned about the different forms of light and what they are used for. We learned how and why light is created. We learned about the speed of light in a vacuum. After the test we will see what happens when we slow down light somehow or we bend or reflect it.