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# 7.10: Solar Energy on Earth

Difficulty Level: Basic Created by: CK-12
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Practice Solar Energy on Earth

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Just how important is this star?

Almost all energy at Earth's surface comes from the sun. The sun’s energy heats the planet and the air around it. This causes the atmosphere to move and create weather. Sunlight also powers photosynthesis and life on Earth.

### The Sun's Energy

Most of the energy at Earth's surface comes from the sun. Solar energy travels in tiny packets that move in waves. The waves have different wavelengths. Waves with different wavelengths carry different amounts of energy.

#### Photons of Energy

The sun gives off energy in tiny packets called photons. Photons travel in waves. These waves make up electromagnetic radiation. Figure below models a wave of light. Notice the wavelength in the figure. Waves with shorter wavelengths have more energy.

This curve models a wave. Based on this figure, how would you define wavelength?

#### Electromagnetic Spectrum

Energy from the sun has a wide range of wavelengths. The total range of energy is called the electromagnetic spectrum. You can see it in Figure below.

Compare the wavelengths of radio waves and gamma rays. Which type of wave has more energy?

Visible light is the only light that humans can see. Different wavelengths of visible light appear as different colors. Radio waves have the longest wavelengths. They also have the least amount of energy. Infrared light has wavelengths too long for humans to see, but we can feel them as heat. The atmosphere absorbs the infrared light. Ultraviolet (UV) light is in wavelengths too short for humans to see. The most energetic UV light is harmful to life. The atmosphere absorbs most of this UV light from the sun. Gamma rays have the highest energy and they are the most damaging rays. Fortunately, gamma rays don’t penetrate Earth’s atmosphere.

### Vocabulary

• electromagnetic radiation: Energy transmitted through space as a wave.
• electromagnetic spectrum: The total range of wavelengths of energy from the sun.
• infrared:Electromagnetic waves with frequencies between radio waves and red light.
• photon: A tiny packet of energy given off by the sun that travels in a wave.
• ultraviolet (UV): Electromagnetic radiation having wavelengths shorter than the violet.
• visible light: Wavelengths of energy that are the only ones that humans can see.

### Summary

• Ultraviolet radiation has the highest energy; infrared the lowest.
• Solar energy travels in photons. Photons travel in waves, which make up electromagnetic radiation.
• Visible light is the wavelengths of light humans can see.

### Practice

Use these resources to answer the questions that follow.

The Electromagnetic Specturm at http://www.youtube.com/watch?v=kfS5Qn0wn2o (2:15)

1. What is the electromagnetic spectrum?
2. Which waves have the longest wavelengths?
3. What has the shortest wavelengths?
4. What is the visible spectrum?
5. Why is the visible spectrum important?
6. What pattern is unique to hydrogen?

### Review

1. What is a photon? How does energy travel as photons?
2. What is visible light? What has longer wavelengths than visible light? Shorter wavelengths?
3. What is the electromagnetic spectrum?

### Notes/Highlights Having trouble? Report an issue.

Color Highlighted Text Notes

### Vocabulary Language: English

Energy transmitted through space as a wave.

electromagnetic spectrum

Total range of wavelengths of energy from the Sun.

infrared

Electromagnetic waves with frequencies between radio waves and red light.

photon

Tiny packet of energy given off by the Sun that travels in a wave.

ultraviolet (UV) light

Electromagnetic radiation having wavelengths shorter than the violet.

visible light

Wavelengths of energy that are the only ones that humans can see.

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