What is Visible Light?
Lesson 3 of 11
Objective: SWBAT explain that light can be considered an electromagnetic wave.
This lesson is all about building student's knowledge about visible light so they can create and make spectroscopes in a future lesson. I use direct instruction in this lesson for most of the class period in order for students to gain an understanding and more background knowledge of light waves. While I orally provide information to students, students also take notes and copy an electromagnetic spectrum into their science notebooks. As I talk and show pictures, students copy the important information into their science notebooks.
I begin this lesson by reminding students that we've learned that light can be thought of as a wave – light is a form of an electromagnetic wave.
I remind students that an electromagnetic wave is a type of wave that can travel through empty space. Unlike sound waves, which need "something" to travel through (for example, water or air), electromagnetic waves are able to travel through "emptiness" or a vacuum.
Next I show students this picture from visible light 1.
It shows different kinds of electromagnetic waves. I tell students that engineers use electromagnetic waves for many different purposes. Gamma rays (nuclear power plant radiation), x-rays, light, microwaves, and radio waves (including cell phone waves) are all electromagnetic waves. What makes all these waves different from each other are their wavelengths and frequencies.
Next, I ask students if they can recall what frequency is? That's right! The frequency of a wave is the number of times a crest occurs each second. Some waves have really big — or even really small — frequencies. If a wave has a higher frequency (many waves in a certain amount of time), it has more energy. And, if a wave has a smaller frequency (fewer waves in a certain amount of time), it has less energy.
Next, I show another picture from visible light 2 and direct students to see if they can figure out which waves have the most energy. I ask questions like: Which waves do you think are the most powerful?
I point out that gamma waves have very high frequencies and, consequently, have a lot of energy. This extreme amount of energy is one reason why gamma waves are very dangerous if improperly used.
I ask students if they have ever had an x-ray? X-rays are not as strong as gamma rays, but they are still very powerful. A sunburn? Have any of you ever burned your skin when out in the hot sun (or overcast as well) too long? Sunburns come from ultraviolet light, which we cannot see, but can still burn our skin. Radio waves and microwaves have a smaller frequency, so they are much less powerful than x-rays or ultraviolet light. Waves are fascinating, that's for sure!
I lead a brief discussion about light waves. I remind students that we know that waves with high frequencies have a lot of energy. And, the waves that have smaller frequencies have less energy — think of these wave types as energetic waves that move very fast and lazy waves that move slow.
I then tell students that we cannot see most electromagnetic waves. The small section of the spectrum with the waves that we can see is called the visible spectrum, and the wavelengths that we can see allow us to see the colors of red, orange, yellow, green, blue, indigo, violet — the colors of the rainbow! We do not usually think of visible light (the visible spectrum) as being an electromagnetic wave, but it is.
To wrap up this lesson, I ask students to reflect and think about what they learned in today's lesson. I ask a few students to volunteer something new they learned. If student's don't mention it, explicitly point out that they learned that visible light is an electromagnetic wave and the only electromagnetic wave we can see. They are also only a small portion of the overall spectrum of electromagnetic waves.