A rainbow is caused by the same physical phenomenon that is behind the prism: the dispersion of light. In dispersion, white light is separated into its constituent colors, from red to green to violet. Read the text aloud
How rainbows form
You can only see a rainbow when you are facing away from the Sun and looking relatively low toward the horizon at air that is humid—full of water droplets. But what causes the effect of the rainbow? The water droplets disperse the white sunlight, refracting the red light rays less than violet light rays. The refraction occurs at the interface between air (n = 1) and water (n = 1.33). Inside the water droplets, the light rays also reflect internally, because the rays strike the inside back surface of the droplet at an incidence angle greater than the critical angle. The violet light rays emerging from the water droplet travel closer to parallel with the ground; the emerging red light rays travel more directly toward the ground. Read the text aloud Show Dispersion angles are small in a rainbow
The rainbow is created because your eyes are seeing light rays of different colors coming from different water droplets—either higher or lower in the sky. The red light in a rainbow comes to your eyes from the highest water droplets, because the droplets have refracted the red light by the least angle. Violet light in the rainbow comes from the lowest water droplets, because the violet light rays were bent the most by refraction. That is why red is always on top of a rainbow; violet is at the bottom. Read the text aloud
Double rainbows are caused by two internal reflections inside a water dropletThe same water droplets that produce a rainbow can also produce a second rainbow—higher in the sky than the primary rainbow—called a double rainbow. A double rainbow is produced when sunlight inside the water droplets undergoes two internal reflections, not one. Because there are two internal reflections, the relative directions of the colors in a double rainbow are inverted with respect to the primary rainbow; i.e., the double rainbow has red at the bottom while the primary rainbow has red at the top. A double rainbow is much fainter than the primary rainbow because of the added losses
resulting from the additional reflection. Read the text aloud
Does violet light or red light travel faster in glass? Show

Previous Page Next Page643