<< Back to Lessons Index

Science_Lab_Yellow / Lesson 5: How Do Light Waves Travel

Light Waves Travel

What will we be learning today?

  • In this lesson, we are going to learn how light waves travel.

  • How Do Light Waves Travel?

    Connect both ends of a wire to a battery, then put a compass near the wire. The compass needle moves. The electric charges flowing through the wire create a magnetic field that affects the compass. This is an example of electromagnetism (i lek troh MAG ni tiz uhm).


    Electromagnetism refers to forces that come from electricity and magnetism. When an electric charge moves in a magnetic field, it produces electromagnetic energy.


    In the 1850s, James Clerk Maxwell concluded from his work that light is electromagnetic energy. The electrical and magnetic parts of the energy can carry themselves as a wave moving through space. Electromagnetic waves can travel without matter or through matter.


    Electromagnetic waves vibrate back and forth across (perpendicular to) the direction in which light travels. Water waves are usually used as models for light waves. The wavelength is the distance from crest to crest. However, light is not just one wavelength. It is many wavelengths. The colors of light are different wavelengths. A prism refracts the different wavelengths different amounts.




      
    James Clerk Maxwell discovered that light is electromagnetic energy. A prism refracts the different colors, or wavelengths, in different amounts.


    However, all the wavelengths of light travel through empty space at the same speed-over 300 million meters per second. Light slows down when it travels through matter. However, it always travels much, much faster than sound. That's why you see a lightning flash before you hear the thunder.


    Since Maxwell's work, scientists have formed another idea of how light travels. Rather than as a smooth vibrating wave, perhaps light travels as tiny bundles of energy. Scientists call the bundles photons.


    Waves or photons? Scientists use both models to explain light. For example, your eye picks up only so many photons of light at any instant. We can see the wavelengths of light that make up the colors of light.




    However, there are wavelengths longer than red light and shorter than violet. We cannot see these wavelengths. Together all these wavelengths of light, the ones we see and the ones we cannot see, are called the electromagnetic spectrum

    Which kind of wave is the shortest? The longest?


    Although we cannot see wavelengths longer than red or shorter than violet, we can detect them, and we can use them in many ways. One way to detect some of this "invisible light" is by using a spectroscope.





    Instruments such as this spectroscope allow us to detect forms of light we can't see. This image taken by the spectroscope, analyzes the light coming from an object.


    Now complete your worksheet!