How Does Light Move?

Lesson Plan - Get It!

Audio:

• What do you think happens to light when it hits a window or a door?

Write a sentence explaining what you think happens when light runs into a window, and a sentence explaining what you think happens when light runs into a wooden door. Hold on to these sentences. You will check your answers at the end of this section.

In this lesson, you will study how light moves. Before you begin, take a few minutes to review what you already know about light.

• What is light?
• How does light travel?

Light is energy and has the properties of both a wave and a particle. Light particles are called photons. Light travels as transverse waves. These waves move extremely fast, at more than 186,000 miles per second!

Light waves travel in a straight path called a ray. A group of rays is called a beam.

Unlike sound, light cannot travel through all forms of matter. When a ray of light hits a solid or a liquid, it does one of four things: it is reflected, refracted, transmitted, or absorbed.

When light is reflected, it bounces off of an object.

Items that reflect light include mirrors, most metals, and glitter.

When a wave of light reflects off an object, it is reflected back at the same angle at which it hits the object. To learn more about how light reflects light, watch this How Mirrors Work | A Moment of Science | PBS video by A Moment of Science PBS:

Name one example of how light can be reflected off an object.

Sometimes a ray of light hits an object and is refracted.

Watch this Bending the light - physics experiment video by Coolphysicsvideos Physics to find out what happens to light when it is refracted (NOTE: Video is silent):

•  What happened to the laser when it was pointed at the glass of water?

When the laser was pointed at the glass of water, it appeared to bend. When a ray of light is refracted, it still travels through the object, but it changes in the process.The amount of bending that occurs depends on the density of the material the light enters, the wavelength of the light wave, and the angle at which light enters the object.

Certain objects cause light to bend as it travels through the objects. Some objects that cause light to refract include water, plastic, and glasses.

When light is refracted, it travels through an object, but changes in the process by becoming bent.

When light is transmitted, it is also able to travel through an object.

The difference with transmission is the light passes through the object at the same speed and direction as it entered.

Finally, sometimes when a light ray hits an object, it neither passes through nor is reflected off the object. Sometimes the object absorbs the light.

When an object absorbs light, the energy from the light is absorbed as heat. When an object absorbs light, no light passes through to the other side.

Look at the images in the beginning of the lesson.

• What happens to light when it hits the window?
• What happens to light when it hits the door?

If you are still uncertain of the answer, get a flashlight and shine it at a window and a door in your home.

• What happens?

Depending on the angle you use to shine the light through the window, the window may either transmit or refract the light. The door should absorb the light.

When you are ready, move onto the Got It? section to continue learning what happens to light when it comes into contact with different forms of matter.