Light and Optics

1. Light and Optics Chapter 22, 23

2. Light as an Electromagnetic wave • Light exhibits behaviors which are characteristic of both waves and particles • Interference, Doppler effect • Electromagnetic waves are waves of changing electrical and magnetic fields. • A changing electrical field will produce a magnetic field. • They travel at 3.00*108 m/s • First detected by creating a rapidly moving electrical charge and detecting the magnetic field a distance away by using a loop of wire.

3. Electromagnetic spectrum • Electromagnetic waves can be produced over a wide range of frequencies • Other EM waves: • Radio, microwaves, infrared, ultraviolet, x-rays

4. Practice • Calculate the wavelength of a 60Hz EM wave, a 93.3 MHz FM radio wave, and a visible red laser of 4.74*1014 HZ • 5.0*106m, 3.22m, 6.33*10-7m

5. Speed of light • First attempted by Galileo using mirrors • Ole Roemer used the period of a moon in Jupiter's Orbit to prove the speed of light was finite. • Albert Michelson Used a rotating mirror and light source to finally prove light moves at a speed of 2.9979*108m/s or 3.00*108 m/s.

6. The ray Model of light • Light travels in … • Straight lines • The straight line paths that light travel in are called Rays • Light travels in every direction from the source. • Geometric optics-describing aspects of light by using the ray model • See smartbooknots

7. Refraction • Index of Refraction • Light travels at c = 3.00 *10 8 m/s in a vacuum • The speed decreases as it passes through other substances. • The ratio between the speed of light in a vacuum and the speed of light in another substance is called the index of refraction • n = c / v • The higher the index, the slower light is traveling

8. Refraction • Refraction is the bending of light • Light bends toward the normal when passing into a more dense medium (higher n value) • Light bends away the normal when passing into a less dense medium (lower n value) • Light bends more as the angle of incidence increases. Angle of incidence is often written as Θ1 Angle of refraction is often written as Θ2

9. Snell’s Law • The angle of refraction depends on the speed of light in the two media and the angle of incidence • n1 (sin Θ1) = n2 (sin Θ2) (Snell’s Law) • Known as the law of refraction

10. Example • Light strikes a flat piece of glass at an incident angle of 60.0 o . In the index of refraction of the glass is 1.50 What is the angle of refraction in the glass, and at what angle does the ray emerge from the glass?

11. Total internal Reflection • When light passes from a more dense material to less dense material, at a particular incident angle the light will skim across the surface. • This angle is the critical angle • Sin Θc = n2 / n1 • For any incident angle greater than this, no light is refracted and there is total internal reflection.

12. Total internal Reflection • Many optical instruments such as binoculars use total internal reflection. • Prisms are used to reflect light • Better than using mirrors because less light is lost. • Fiber optics- glass or plastic fibers that internally reflect light to transmit it from one place to another. • Telecomunications • Medical • Bronchoscope

13. Physics of Diamonds • Diamonds achieve their brilliance partially from total internal reflection. Because diamonds have a high index of refraction (about 2.3), the critical angle for the total internal reflection is only about 25 degrees. Incident light therefore strikes many of the internal surfaces before it strikes one less than 25 degrees and emerges. After many such reflections, the colors in the light are separated, and seen individually.