In this Just-in-Time Professional Development video, science educator Rachel Connolly demonstrates three activities you can use to help students grasp how light travels and that white light is a mix of light frequencies.
Electromagnetic radiation, or light, is a complex concept to understand. Although students experience it all the time, they likely have many misconceptions about the nature of light. Some common misconceptions are that:
Light doesn’t travel; it is only associated with a source or its effects.
The effects of light are always instantaneous.
Light can travel around objects.
A white light source, such as an incandescent bulb, produces light made up of only one color.
Visible light is the only type of light.
Gamma-rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves are completely different things from each other.
Such misconceptions can be difficult to overcome. However, hands-on activities for students can help promote conceptual change. It is important be aware of the preconceptions that students may bring to class and to provide them with repeated activities and adequate time for exploration to help them develop a more complete understanding.
These activities all require that you dim the lighting in your classroom space, so make sure that students have a safe and adequately illuminated path for movement.
Activity #1: The Race with a Beam of Light
Introduce the idea that light travels very quickly with a flashlight, a darkened room, and a clear path from one end of the room to the other. Ask for a student volunteer to race against light. Stand at one end of the room with the student and point the flashlight toward the wall. Have the rest of the class count down from three, at which point you turn on the flashlight and the student runs toward the far wall. Which reaches the wall first: the student or the light from the flashlight? Explain that although the light appears to reach the wall instantaneously, it does have a speed—it is just much, much faster than a person could run.
Activity #2: The Invisible Made Visible
Have students experiment and play with beams of light in a darkened room. Use flashlights and various materials (such as chalk dust or water from a spray bottle) to investigate the fact that light is always moving in a straight line through space even though you may not always see it. Have students use their hands and other materials to intercept the beam of light from the flashlight at various locations.
Activity #3: Explore the Rainbows
Have students consider how light could contain a rainbow of information using a string of white twinkle lights. Have students look at the white lights and ask: Do you see the colors? After some time, have them look at the lights again using spectral glasses or diffraction gratings. Explain how breaking white light into its components shows you more information. Expand the discussion to exploring different regions of the electromagnetic spectrum.