Learn and try: Electromagnetic waves (article) | Khan Academy
Learn about electromagnetic waves, including visible light waves. Explore the ray model and use it to model different behaviors of light.
En bref

Ajouté le
18 mars 2026
Matière et domaine
physics · ac-circuits-electromagnetic-waves
Niveaux scolaires
6e année–9e année (3e)
Type de page
Article
Introduction
Electromagnetic Waves and Light Behavior
- Definition: Electromagnetic (EM) waves are disturbances traveling through the electromagnetic field. They can propagate through a vacuum because the field exists everywhere.
- Speed: All EM waves travel at the speed of light when in a vacuum.
- The EM Spectrum: EM waves exist across a wide range of frequencies and wavelengths. Visible light represents only a small portion of this spectrum.
- Ray Model: Because light travels in straight lines, its path can be represented using the ray model.
- Interactions with Matter: When EM waves encounter a boundary between materials, they undergo three primary behaviors:
- Reflection: The wave bounces off the surface and changes direction.
- Transmission: The wave passes through the boundary into the new material.
- Absorption: The wave's energy is converted into thermal energy or another form within the material.
- Color Perception:
- Human color vision is facilitated by cone cells in the eye, which are sensitive to different energy levels (frequencies) of light.
- Objects appear colored because their surfaces reflect specific frequencies of light while absorbing others.
- "White" light is a mixture of all visible colors; rainbows occur when water droplets refract (bend) light, separating it into its constituent colors.
- "Black" is perceived when an object absorbs most or all visible light. A "true black" object (absorbing 100% of light) would appear as a flat, 2D silhouette lacking depth or texture.
- Mirrors appear to have no color because they reflect most frequencies of light equally, reflecting the colors of the objects in front of them.
Avis de la communauté
Pas encore d’avis publiés. Soyez le premier à partager votre expérience.