1 / 18

11.1 – Refraction of Light

11.1 – Refraction of Light. What is Refraction?. Refraction is a property of light in which the speed of light and its direction of travel change as it passes from one medium to another. Air. Water. How does refraction occur?.

miranda-harvey
Download Presentation

11.1 – Refraction of Light

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 11.1 – Refraction of Light

  2. What is Refraction? • Refraction is a property of light in which the speed of light and its direction of travel change as it passes from one medium to another Air Water

  3. How does refraction occur? • Light travels in a straight line and at a constant speed as long as the medium it is travelling in remains the same • When light travels from one medium to another, however (e.g., from air to water), the light rays bend, or refract • This means that both its direction and speed changes

  4. How does refraction occur? • Light travels as a wave • Crests and troughs of waves can be thought of as wave fronts, with rays perpendicular to them showing the direction the wave is travelling in

  5. How does refraction occur? • Think of a marching band: • The mud is sticky, so students cannot march as fast in it • As each student reaches the mud, he or she slows down • The slower students “pull” the line back and cause a bend in the line, representing the wave front • As a result, the direction in which the entire row is marching changes – light behaves the same way

  6. Fermat’s Principle • The exact path of light as it travels from one medium to another can be found by applying Fermat’s Principle: When light travels from one point to another, it follows the path that will take the least time. • In a single medium, the path that takes the least time is a straight line • When travelling from one medium to another, the path that takes the least time is not a straight line

  7. Fermat’s Principle • Compare the dashed line with the solid, bent line going from point A in the air to point B in the water • In air, where light travels faster, the solid line is longer than the dashed line • In water, where light travels slower, the solid line is shorter than the dashed line

  8. Fermat’s Principle • Light travels a longer distance in air and a shorter distance in water than it would if it followed a straight line • Following the bent path (solid line) takes less time than following the straight path (dashed line).

  9. Describing Refraction Using Rays • Mostly similar terminology to reflection • The refracted ray is the ray that is bent upon entering a second medium • The angle of refraction, R, is the angle between the normal and a refracted ray

  10. The Direction of the Refracted Ray • If a light ray travels from a medium in which its speed is faster (such as air) to a medium in which its speed is slower (such as water), the refracted ray bends towards the normal

  11. The Direction of the Refracted Ray • If a light ray travels from a medium in which its speed is slower to a medium in which its speed is faster, the refracted ray bends away from the normal

  12. The Direction of the Refracted Ray • In summary: • Faster medium  Slower medium = Bends towards the normal • Slower medium  Faster medium = Bends away from the normal

  13. The Index of Refraction • How much a light ray refracts is determined by how much the speed of light changes as it travels from one medium to another • In a vacuum (such as space), the speed of light is 3.00 x 108 m/s • The speed of light is less in any other medium • e.g., the speed of light in water is 2.26 x 108 m/s • It is inconvenient to use these large numbers to describe relative speeds, so we use the index of refraction instead

  14. The Index of Refraction • The index of refraction is the ratio of the speed of light in a vacuum to the speed of light in a given medium

  15. The Index of Refraction • Example: calculate the index of refraction of water if light travels through it at 2.26 x 108 m/s

  16. Using the Index of Refraction (Found on pg. 454)

  17. Dispersion • Dispersion is the process of separating colours by refraction • Each colour of light travels at a slightly different speed in any medium except a vacuum (where they all travel the same speed) • Can see this by shining white light into a prism

  18. Dispersion • White light contains all the wavelengths (i.e., colours) of visible light • When white light is shined into a prism, it refracts twice – once when it enters, and once when it leaves • As it exits, the light is separated into a spectrum of colours • Blue light bends more than red light, so it must be travelling at a slower speed

More Related