How does the temperature affect the diffraction of light in a mirage ?
http://www.scientificamerican.com/article.cfm?id=what-causes-a-mirage
Temperature affects the diffraction of light in a mirage by creating variations in the refractive index of the air. To understand this, let's delve into the explanation.
When light passes through a medium, such as air, it can change direction due to its interaction with the atoms or molecules in that medium. This change in direction is known as refraction. The amount of refraction depends on the refractive index of the medium, which is a measure of how much the speed of light decreases in that medium compared to its speed in a vacuum.
In the case of a mirage, which is an optical illusion where distant objects appear displaced or distorted, temperature plays a significant role. Mirages typically occur in hot environments, such as deserts or hot pavement. Let's see how temperature affects the diffraction of light in this context:
1. Temperature gradient: When the ground is heated by the sun, the air close to the ground gets hotter. This creates a temperature gradient, which means that the temperature decreases as we move higher above the ground.
2. Variations in refractive index: The refractive index of air is directly influenced by its temperature. As the temperature increases, the refractive index decreases, and vice versa. In the case of a temperature gradient near the ground, there will be areas of air with different refractive indices, forming layers.
3. Bending of light: When light encounters a temperature gradient, it changes its direction due to refraction at each layer. This bending of light occurs because light travels at different speeds through layers with different refractive indices.
4. Total internal reflection: In a mirage, the bending of light rays can be quite significant. As the light travels through the layers of varying refractive indices, it reaches a critical angle where the refracted light ray is almost parallel to the ground. At this critical angle, total internal reflection may occur, causing the light ray to bounce back towards the ground.
5. Image formation: The total internal reflection creates an illusion of a virtual image, making objects appear to be on the surface of the road or ground. This phenomenon leads to the mirage effect, where distant objects seem displaced or distorted.
In summary, the variation in temperature near the ground creates a temperature gradient, resulting in different refractive indices for each layer of air. This causes light to bend as it passes through the layers, leading to total internal reflection and the formation of a mirage.