Lesson Plan - Get It!
- How fast does light move?
When you sit in the sun to "catch a few rays," you're probably not being literal!
- Do you think light travels fast or slow?
Tell your teacher or parent.
Light could easily beat the fastest car in a NASCAR race, and can travel from New York to London faster than any jet!
Light travels at a speed of 186,000 miles per second! It takes light less than eight and a half minutes to travel 93 million miles, from the sun to earth. Now that's fast!
Light travels as a transverse wave. To learn exactly what a transverse wave is, watch the video Physics - Waves – Introduction. by expertmathstutor (below):
What is the difference between a transverse wave and a longitudinal wave?
- In a transverse wave, the vibrations are perpendicular to the direction the wave is traveling.
- In a longitudinal wave, the vibrations are parallel to the direction the wave is traveling.
Get a Slinky, if you have one. Hold one end of the Slinky while your teacher or parent holds the other end a few feet away from you. Hold your end still while your teacher or parent moves their end up and down. You have just created a transverse wave. Discuss what you observed about the movement of the Slinky with your teacher or parent.
There are four terms you need to know when studying a transverse wave: crest, trough, wavelength, and frequency. These terms were also discussed in the video.
A crest is the highest point on a wave, and a trough is the lowest point on a wave.
Wavelength describes the distance between two waves. A wavelength can be measured from any point on a wave, as long as it is measured to the same point on the next wave. Point to where the wavelength is labeled below:
When measuring wavelengths, use the metric units millimeters and centimeters unless another unit is specified. You have to know what a wavelength is in order to find the frequency.
Frequency is the number of wavelengths (or cycles) in a wave during a fixed period of time, usually seconds.
Look at the picture below, illustrating one second.
- What is the frequency of the wave?
That's correct! The light wave pictured has a frequency of two cycles per second because there are two full wavelengths pictured.
The frequency of a light wave is proportional to its energy. A high-frequency wave has high energy. A low-frequency wave has low energy.
- Do the waves pictured above have high or low energy?
Share your answer with a teacher or parent and explain your reasoning.
Think you understand all the parts of a light wave? Move on to the next section to find out!