This is the final regular Investigation of the LabLearner CELL Light and Optics. In it, students will continue their exploration of the Visible Spectrum and be introduced to the entire Electromagnetic Spectrum.

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A. Begin the Investigation by reviewing the concepts from Investigation Four. Ask students to refer to their Scientist’s Glossary for the definitions of the terms as they are used.

1. Use this slide to review the Visible Spectrum. Initiate a discussion by asking students to recall the answers to the following questions:

a. Ask students: Can you detect white light from the Sun? Yes. Can you detect the colors of the Visible Spectrum? Yes

b. Ask students: How is white light separated into the colors of the Visible Spectrum? When white light is refracted, for example by a prism or by raindrops during a storm, it can be separated into the Visible Spectrum.

c. Ask students: How do the wavelengths of the light waves of the Visible Spectrum differ from one another? The light waves differ by possessing different wavelengths.

d. Ask students: Compare the wavelengths of violet and red light? Violet light has a shorter wavelength, 400 nm, than red light which has a wavelength of 700 nm.

e. Ask students: What is the wavelength of green light? Student answers will vary. The wavelength of green light is intermediate between the wavelengths of violet and red light. Green light has a wavelength of approximately 550 nm.

f. Ask students: Does the Visible Spectrum contain only certain colors of light? The Visible Spectrum contains an infinite number of colors. The colors that are typically named are simply those that are most easily recognized as specific colors. The Visible Spectrum is a continuum of colors that changes continually because of slight changes in wavelength from wave to wave.

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2. Review absorption and transmission of light by asking students to recall the answers to the following questions:

a. Ask students: What occurred when the white light from the flashlight was shown through the red, blue, and green filters?  Many wavelengths of the Visible Spectrum were absorbed by each of the filters. Some wavelengths were transmitted through the filters.  The combination of wavelengths transmitted through the filter produced light of a certain color. For example, the shade of red seen through the “red” filter was produced by a combination of light of red, dark blue, and violet wavelengths.

b. Ask students: What is the term that describes what happened to the color light that was not absorbed by the red, blue, and green filters? The light that was not absorbed was transmitted through each of the filters.

c. Ask students: What happened when the light was shown through two different color filters? Some wavelengths of light were absorbed by the first filter and some were transmitted.  Some of the wavelengths of light that were transmitted through the first filter were absorbed by the second filter.  Some were transmitted. The color of light that was seen on the white paper was the result of the wavelengths of light that were transmitted through BOTH filters.

d. Ask students: Can you describe the relationship between the light waves that are absorbed or transmitted by a colored filter? Light waves are either absorbed or transmitted by a filter. Those waves that are not absorbed are transmitted.

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B. Introduce students to the Electromagnetic Spectrum using this slide.

1. Orient students to the Electromagnetic Spectrum by pointing out that they are looking at a scale, where short wavelengths are on the left and longer wavelengths are on the right. As the scale goes from left to right, the wavelength increases. 

Show students how the Visible Spectrum lies within the Electromagnetic Spectrum. Inform students that the Electromagnetic Spectrum includes not only the Visible Spectrum but additional types of energy waves with which they may be familiar. As the different types of energy waves are discussed, ask students to record the name of each wave in the diagram of the Electromagnetic Spectrum in their Student Data Record.

a. Ask students, What do you know about radio waves? Student answers may vary. Radio waves, including AM, FM, and televisions waves, are a type of energy wave that encode radio and television broadcasts and carry them to your radio and television.

b. Ask students, What do you know about microwaves? Student answers may vary. Microwaves are a type of energy wave produced by microwave ovens that cook foods by heating water in the food.

c. Ask students, What do you know about infrared waves? Student answers may vary. Infrared waves are a type of energy wave produced by the Sun that warms our skin on a bright summer day.

d. Ask students, What do you know about ultraviolet (UV) waves? Student answers may vary. Ultraviolet waves are a type of energy wave produced by the Sun that causes sunburn by killing the outer layer of skin cells. If a person suffered from numerous sunburns over many years, ultraviolet waves could eventually cause skin cancer.

e. Ask students, What do you know about x-rays? Student answers may vary. X-rays are a type of energy wave that is able to penetrate a person’s body so a physician or dentist can produce an image of a broken bone or a decayed tooth. While the limited use of X-rays is beneficial, overexposure could prove harmful.

f. Ask students, What do you know about Gamma rays? Student answers may vary. Gamma Rays are a type of energy wave produced by nuclear explosions and the Sun. Gamma Rays from the Sun do not reach the Earth’s surface. Gamma Rays are capable of killing cells which is why they can be used in medicine to kill unhealthy or cancerous cells in the body.

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2. Begin a discussion of how the waves of the Electromagnetic Spectrum can all be differentiated by their different wavelengths.

a. Inform students that the Electromagnetic Spectrum is a continuum of waves whose wavelengths gradually and seamlessly change. Just like the Visible Spectrum, each type of wave is not a specific wavelength but a range of wavelengths that increases or decreases gradually.

b. Inform students that the wavelengths of the wave energies extend from very long wavelengths to exceedingly short wavelengths.

• Radio waves possess the longest wavelengths of approximately 1,000 meters or about one half mile.

• Gamma rays possess the shortest wavelengths of approximately 0.0000000000001 meters.

• All other wavelengths fall somewhere between these two extremes.

c. Correlate the previous discussion of the different types of wave energies of the Electromagnetic Spectrum and their effect with their approximate wavelengths.

• The energy of the waves increases as the wavelength decreases.

• Radio waves are not thought to be harmful and have the longest wavelength.

• As the wavelength of the waves decreases, the energy increases and the effect becomes more pronounced.

• Gamma Rays are the most dangerous energy waves, and can produce serious harm or even death to anyone who is exposed to them. However, physicians who have been specially trained can use them to treat some types of cancer (radiation therapy).

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C. Begin a discussion of our perception of the wave energies of the Electromagnetic Spectrum.

1. Ask students, Can we detect or perceive any of the wave energies of the Electromagnetic Spectrum directly using any of our senses? Student answers may vary. Most of the wave energies of the Electromagnetic Spectrum are detected or perceived only indirectly. Only visible light is perceived directly by one of our senses, sight.

2. Ask students the following questions.

a. Ask students: How can you detect radio waves? Student answers may vary. We can listen to the radio and view television broadcasts but we cannot detect radio waves directly.

b. Ask students: How can you detect microwaves? Student answers may vary. We can detect the heat in food that has been heated by microwaves but we cannot detect microwaves directly.

c. Ask students: How can you detect infrared waves? Student answers may vary. We can feel the warmth caused by the Sun’s infrared waves as they fall on our skin.

d. Ask students: How can you detect visible light? Student answers may vary. We can detect visible light through our sense of sight.

e. Ask students: How can you detect ultraviolet waves? Student answers may vary. Ultraviolet waves can be detected indirectly when we suffer from sunburn on our skin.

f. Ask students: How can you detect X-rays? Student answers may vary. Only the results of X-rays can be detected. The image from an X-ray or the harmful effects of these high energy waves can be detected.

g. Ask students: How can you detect Gamma Rays? Student answers may vary. Only the harmful effects of these high-energy waves can be detected in the form of damage to cells of the body.

h. Ask students to answer Problem 1a in their Student Data Record: 

As the wavelengths of the energy waves decrease from long to short, what can you conclude about whether the energy of each wave increases or decreases? Why? As the wavelengths of the energy waves become shorter, the energy of each wave increases. The effect of each wave on the human body becomes more significant and harmful as the wavelength becomes shorter.

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1. Ask students: What rule describes the absorption and transmission of different wavelengths of the Visible Spectrum by transparent objects? Any wavelengths that are not transmitted must be absorbed by the object. The wavelengths that are absorbed are missing from the wavelengths that are transmitted by transparent objects.

2. Ask students: What rule describes how we perceive the color of a transparent object? Any wavelengths that are not absorbed must be transmitted through a transparent object. The wavelengths that are absorbed are missing from the wavelengths that are transmitted, so the color of the transparent object corresponds to the wavelengths that are transmitted.

• Inform students that when considering the perception of visible light, we perceive only those wavelengths and the corresponding colors that are not absorbed by an object.
• If we look through a transparent object, we perceive only the wavelengths and the corresponding colors that are transmitted by the object.
• Use students’ understanding of the relationship between absorption and transmission of light with transparent objects to introduce perception of color with opaque objects.  Explain that light is not transmitted through opaque objects. Therefore, students should consider the absorption and REFLECTION of light when dealing with the color of opaque objects.
• Remind students that when considering the perception of visible light, we perceive only those wavelengths and the corresponding colors that are not absorbed by an object.
• If we look at an opaque object we perceive only the wavelengths and the corresponding colors that are REFLECTED by the object into our eyes.
• The reflected wavelengths are perceived by our eyes as the color of the object.

E. Inform students that in this Investigation they will explore how our sense of sight is able to perceive the wave energies of the Visible Spectrum.