1. Waves
Teaching Slides, 3.2
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Waves Course, 3.2: Spectra

2. Science Log Q4 week 6 Wednesday:
What is the relationship between the angle of incidence and the angle of reflection with light? What is that called?
The angle of incidence equals the angle of reflection.
This is called the law of reflection.
Waves Course, 3.2: Spectra

3. 1. Rainbows
Share with a partner what you know about rainbows and a question you may have. Think about the following.
What color is light from the Sun?
Have you ever seen light from the Sun spread out as all the different colors in the sky?
Do you know how rainbows form?
Waves Course, 3.2: Spectra

4. 1. Rainbows
When the Sun’s light waves travel through air that has a lot of water drops in it, under some circumstances each tiny droplet can act like a tiny prism.
A prism is a triangular piece of clear glass or plastic with special properties that let it show all the different colors of light that are present.
The water droplets, acting like little prisms, spread out the colors in sunlight into a rainbow.
A rainbow of colors can also be called a spectrum of colors. The plural of spectrum is spectra.
Waves Course, 3.2: Spectra

5. Focus question 3.2 page 37 What do spectra reveal about light?
Waves Course, 3.2: Spectra
Step 1

6. 3. Spectroscopes
This tool can break light into colors, its called a spectroscope.
At one end it has a slit opening where light can enter and at the other end is a piece of plastic with many, many tiny grooves in it.
The plastic is called a diffraction grating, and it can spread light out into it colors much like a prism does.
Waves Course, 3.2: Spectra

7. 3. Spectroscopes
When you get your spectroscope, hold the small end with the round hole (not the slit end) up to your eye and try looking through it at whatever light sources you find in this room.
You should be able to see a slit on the left and a number scale on the right, with a band of light below the numbers.
Waves Course, 3.2: Spectra

8. Spectra
How would you describe the spectrum you see from light coming in from the skylights, sunlight?
It looks like a rainbow
What color in the spectrum appears at the lowest end of the number scale?
Violet
Waves Course, 3.2: Spectra
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9. Spectra
What color in the spectrum appears at the highest end of the number scale?
Red
What is the order of colors in the rainbow, starting at the low end of the scale?
Violet, blue, green, yellow, orange, red.
Waves Course, 3.2: Spectra
Step 4

10. Spectra
ROYGBIV
Waves Course, 3.2: Spectra
Step 1

11. Spectra drawing
Draw each light source. Record a sketch of its spectrum in your notebook page 38, and label the light source.
Waves Course, 3.2: Spectra
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12. Spectra
The spectrum for a light is like its signature. Each kind of light has a unique signature.
The bright lines you see in a fluorescent light spectrum, especially the bright green can help you identify a fluorescent light.
The spectrum is different from the sunlight spectrum.
Waves Course, 3.2: Spectra

13. 5. Analyze the scale
The spectroscope has a scale in it for measuring wavelengths of light waves. The numbers on the scale indicate the wavelength of light along the different parts of the spectrum. The numbers 4, 5, 6, and 7 represent 400, 500, 600, and 700 nanometers, respectively.
Waves Course, 3.2: Spectra
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14. Analyze the scale
What did you find for the longest wavelength of visible light?
About nm
What did you find for the shortest wavelength of visible light?
About nm
Light visible to humans is roughly nm.
Waves Course, 3.2: Spectra
Step 5

15. Wrap-Up/Warm-Up What must happen for you to see an object?
You have to see light from the object. It could be emitted (like a lightbulb or computer screen) or reflected (like a book, pen, or your hand)
What happens when light reflects?
Light waves bounce off a surface. The angle of reflection equals the angle of incidence.
What kinds of surfaces reflect light?
Nearly every single thing! If you can see it, and it is not a source of light, it must be reflecting light.
Waves Course, 3.1: Mirrors
Step 19

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Cover slide: © Sergey Nivens/Shutterstock
Notebook image: © photastic/Shutterstock
Waves Course, 3.2: Spectra