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In the last class we talked about energy transferring kinetically from one thing to another. In other words, moving molecules/atoms bump into other molecules/atoms, which causes them to move faster. This results in the matter heating up. Sound energy is transferred kinetically as well, however the molecules and atoms move in a wave pattern. Energy can also be transferred by radiation.
Electromagnetic waves can travel through a vacuum, unlike sound which must travel through matter. Energy is transferred from the sun to the Earth because the sun radiates energy. Electromagnetic waves have a wide range of wavelengths. We have different names for the different ranges of wavelengths (gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves). The shorter the wavelength, the more energy the radiation has. The more energy the wave has, the more disruptive it can be to the matter it comes in contact with. Below you can see an example of a sheet to color in. You could leave the visible spectrum bar white and have the kids color it in. You could also have them draw things that match the sizes of the wavelengths. There are lots of examples of figures that people have made if you do an image search for the electromagnetic spectrum.
Radio waves have the longest wavelengths. In previous lessons we have talked about some metals sharing their electrons in a cloud which allows them to be good conductors of electricity. Radio waves move these electrons from one side of an antenna to another side and back again. This causes the sides of the antenna alternate between positive and negative charges. I demonstrated this by having the kids sit on the floor and pretending to be atoms. I gave them ping pong balls to represent electrons. Then I had the kids roll the balls in one direction and then in the opposite direction a few times.
Microwaves have the next shorter wavelengths. These are the same microwaves in your microwave oven. The walls of the oven keep these waves from escaping. Microwaves rotate molecules like water, which have a dipole moment. The side of the water molecule that has the two hydrogen atoms has a positive charge and the oxygen side has a negative charge. You can see below how the wave alternates pulling the positive and negative sides of the molecules.
I crocheted these water molecules. The pattern is below.
Water Molecules Pattern
Make 2 halves for oxygen and 4 halves for hydrogen. Sew the halves together almost completely, stuff, and then finish sewing. Then sew the two hydrogen atoms onto the oxygen atom. I used Swish Worsted yarn from Knit Picks to make these water molecules.
ch 4, slp st to form a loop and work the first rnd into the loop
rnd 1: 7 sc
rnd 2: 14 sc
rnd 3: 21 sc
rnd 4-7: 28 sc
rnd 1: 5 sc
rnd 2: 10 sc
rnd 3: 10 sc
Atoms in molecules can move a little without breaking their bonds. This is the type of movement that occurs to all molecules when they are exposed to infrared radiation. This movement causes matter that is exposed to infrared radiation to heat up. I’ve made these molecule models from pipe cleaners and beads. The beads represent the atoms in the molecule.
The atoms can move towards each other to pinch together or rock with each other in the same plane.
The atoms can also move towards and away from the molecule. This is why I made the pipe cleaners into a spring shape so I could stretch and squash them. At the bottom of the picture you can see the atoms moving in and away from the molecule together and separately.
Infrared, Visible Light, and Ultraviolet
Some infrared, all visible, and some ultraviolet light get absorbed by atoms and excite their electrons. An electron is excited when it moves into a higher electron shell (orbit). You can find an explanation of electron shells in this post. This electron will fall to a lower shell after it has been excited, and when it does it gives off radiation with a longer wavelength than what it absorbed. Infrared and visible light will decay to infrared. This causes matter to heat up. Absorption of some UV light will lead to visible light being emitted when the electron falls to a lower electron shell. This is why some things seem to glow under a black light. The item is absorbing UV light that we can’t see, and emitting visible light. This is fluorescence.
Why are things different colors?
White light is made up of all the colors we can see. It can be split into colors which are visible as a rainbow when it is sunny right after it rains. Different colors of visible light have different wavelengths. I’ve modeled this with pipe cleaners which represent the different colors of light.
Below is a model of a hydrogen atom. I’m using this as an example to explain what happens when atoms absorb visible light. Hydrogen does not absorb yellow light. It is reflected back when it encounters hydrogen atoms. Red light and violet light are absorbed and move the electron up to another orbit. All matter absorbs and reflects some portion of visible light. The light that is reflected back makes up the colors that we see. Something that is red, for example, absorbs orange, yellow, green, blue, indigo, and violet light and reflects red. Cells in our eyes absorb the red light, and our brain interprets the color of the object to be red.
What we call visible light is what humans can detect. Some birds and insects can see some UV light and snakes can detect infrared radiation. Some bird feathers have different UV color patterns in males and females which may help with mate selection. It may also help them look for food. Snakes use their ability to detect infrared to hunt at night.
Some Ultraviolet Light and X-rays
The shortest wavelengths of ultraviolet light and X-rays don’t just excite atoms, they actually force them away from the nucleus of an atom. This is dangerous to humans because it can cause changes in DNA which can lead to cancer.
Gamma rays also remove an electron from the nucleus of an atom, however this electron has so much energy that it also can force an electron from another atom away from its nucleus. The shortest wavelengths of gamma rays will actually produce a new electron when they interact with a nucleus. Gamma rays will also cause DNA damage.
The sun produces all of these types of radiation. However, gamma rays are produced by the nuclear fusion reactions in the core of the sun and they do not escape the sun’s atmosphere. X-rays and most UV is absorbed by the Earth’s atmosphere before it ever reaches Earth’s surface. However, some UV light does reach the surface and that is why it is important to reduce your sun exposure. Some sun exposure is necessary to make vitamin D. However, for people with lighter to darker skin the range of time in the sun at noon needed to produce enough vitamin D, ranges from 5 to 30 minutes per day. Skin cancer can occur in anyone, so please practice sun safe behaviors. Wear sun block and/or protective clothing at peak sun times if you are out for longer than the time needed for you to make enough vitamin D for the day.
For more STEAM crafts and activities, take a look at my Pinterest board.