Recall: Light travels in a straight line and at a constant speed as long as the medium it is traveling in is the same. When light travels from one material to another, it can bend. Refraction: ________________________________________________________________ _____________________________________________________________________________. Example: When driving a golf cart you hit some mud or gravel. What happens? The front wheels suddenly slow down, but the back wheels keep going and the golf cart twists around. When light travels from one medium into a different medium, both speed and direction may change. Examples: Describing Refraction Using Rays Most of the terms to describe refraction are the same as the terms for reflection. However, there is a third ray called the REFRACTED RAY. Refracted ray is the ray that is bent upon entering a second medium. The incident ray is divided into two rays – one that reflects and one that refracts. The new angle is called the ANGLE OF REFRACTION. Air Water Angle of Refraction (R): Refracted Ray: Note: All angles are measured between the ray and the normal. If the angle of Incidence is zero, there is no refraction. The direction of the Refracted Ray A light ray travels from a medium in which its speed is ________(such as air) to a medium in which its speed is _________ (such as water); the refracted ray bends __________ the normal. Air Water If a light ray travels from a medium, in which its speed is _________ to a medium in which its speed is ___________, the refracted ray bends _____ from the normal. Glass Air How much a light ray refracts is determined by the extent of the change in speed of light as it travels from one medium to another. When light passes from one medium to the next and the change in the speed of light becomes greater, the angle of refraction becomes greater. The speed of light is 3.00 x 108 m/s in a vacuum, such as space. The speed of light is less than 3.00 x 108 m/s in any other medium. Index of Refraction: ________________________________________________ _________________________________________________________________. Partial Reflection and Refraction Some of the light that is travelling from one medium into another is reflected and some is refracted at the boundary between the media. Example: Sometimes when you look out a window, you see what is outside as well as your own reflection. The amount of reflection compared with the amount of refraction depends on the angle of incidence as well as the relative indices of refraction of the two media. Dispersion Dispersion: _____________________________________________________. Each colour of light travels at a slightly different speed in any medium. Only in a vacuum do all the wavelengths of light, and all other forms of electromagnetic waves, travel at the same speed – 3.00 x 108m/s. When white light is ``separated`` into a rainbow it has been dispersed. The rainbow is called the SPECTRUM. The spectral colours are: _____________________________________________. Dispersion is the result of refraction: Each colour is bent at a slightly different angle with red being bent the least and violet being bent the most. If the spectrum is directed through a converging lens, it will appear white – this is called recomposition. The indices of Fraction of various substances. Sample problem: Calculate the speed of light in fused quartz. Practice problems 1. Calculate the speed of light in flint glass. 2. Calculate the speed of light tin crown glass. 3. A.)The speed of light in a solid is 1.24 x 108 m/s. Calculate the index of refraction. B.) Use the table to identify the substance.