Because glass is denser than air, when a light ray strikes the prism’s surface, it bends towards the normal. The angle of the prism is represented by D in the diagram.Īccording to Snell’s law, light bends towards normal when travelling from a rarer medium to a denser medium, and away from normal when travelling from a denser medium to a rarer medium. This angle is known as the ‘Angle of the Prism.’ Consider a triangular prism with a light beam travelling through it. Refraction and dispersion through a Glass PrismĪ glass prism is made up of three rectangular lateral surfaces and two triangular bases that are all tilted at an angle. The fainter rainbow appears in the same way as the sharper rainbow, except that the light is reflected twice inside the raindrop rather than once.As a result of the twofold reflection, the light exits the raindrop at opposite angles, and we see it above the sharper rainbow. On rare occasions, a double rainbow can be seen, consisting of a bright rainbow with a fainter rainbow above it. We observe wide bands of colour because we only see one colour from each raindrop, as if various moist spots were propagating a different single hue. In this way, each raindrop disperses the white sunlight into its constituent hues. Some of the reflected light escapes the drop and bends as it returns to the atmosphere. Some of the light is reflected back to the observer, while the remainder is released into the atmosphere. As violet light penetrates the raindrop, it bends at a sharp angle. When compared to a glass prism, each raindrop has a different form and substance, but it still affects light in the same way.Īs white sunlight travels from air into a drop of water, the constituent colours of light slow down to varying rates and frequencies. Dispersion of Light and RainbowĪ rainbow appears when it rains and the sun shines at the same moment. Refraction is the bending of a ray when it passes at an angle from one medium into another with a different speed (as when light passes from air to water). At various frequencies and angles, white light splits into its constituent colours.
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