Light Notes

1. Light Notes CP Physics Ms. Morrison

2. ELECTROMAGNETIC WAVES

3. Electromagnetic Waves • Moving charged particles create magnetic fields • Changing motion of charged particle creates expanding and collapsing magnetic field which generates and expanding and collapsing electric field • Travel at 3.0 x 108 m/s through empty space ( c = speed of light) • Travels more slowly through mediums • Energy depends on frequency

4. Electromagnetic Spectrum

5. 7 Types of Electromagnetic Radiation • Radio Waves • Microwaves • Infrared waves • Visible light • Ultraviolet light • X-rays • Gamma rays

6. Radio Waves • Lowest frequency • Longest wavelength • Least energy of spectrum • Carry sound waves

7. Microwaves • Frequencies match natural frequencies of molecules (fats, proteins, etc.) • Causes food molecules to vibrate making the food cook itself • Icebergs give off microwaves • Match natural frequencies of some pacemakers

8. Infrared waves • Heat waves – all animals give off infrared • Uses: • Heat lamps • Night vision • Alcohol breath test • Remote controls

9. Visible Light • Only 1/1,000,000 of EM spectrum • Different frequencies seen as colors (ROY G BIV) • Red light • Lowest frequency (least energy) • Longest wavelength • Violet light • Highest frequency (most energy) • Shortest wavelength

10. Ultraviolet Light • Causes sunburns, damages tissues, and can kill bacteria • UV-B rays more dangerous than UV-A because they have higher frequency

11. X-rays • Produced by high speed electrons slamming into a metal plate • Uses: • Medical X-rays (bones, teeth) • Airport security

12. Gamma Rays • Highest frequency of EM spectrum so highest energy waves of spectrum and greatest penetrating power • Shortest wavelengths of spectrum • Produced by nuclear particles and occur with every nuclear reaction • Used in radiation therapy (kill healthy cells, but kill cancer cells)

13. VISIBLE LIGHT

14. General Characteristics • Frequencies that eye is sensitive to • c = 3 x 108 m/s • c = λf • Transverse wave • Interaction with materials • Transparent – all light transmitted, ex. Clear glass • Translucent – scatters light transmitted, ex. Frosted glass • Opaque – does not transmit any light, ex. Brick

15. Wave Behavior • Behaves like wave when traveling through empty space or through a medium when it does not interact with the medium’s particles • Behave like all other waves: • Reflects • Refracts • Diffracts (ex. Prism – see colors of light) • Interferes • Constructive – produces light bands • Destructive – produces dark bands

16. Particle Behavior • 1900s – discovered that light can act like a particle when it interacts with matter • Certain colors of light produce photosynthesis when light absorbed by green leaves • Certain colors of light shown on metal plates cause electrons to jump of the atoms and create electric current (ex. Solar calculators) • Electrons jump to higher energy levels in atom when absorb energy, when return to ground level will emit specific color of light

17. Quantum Theory • Explains how light interacts with matter • Photon = quantum of light energy (packet of light energy) • Photon’s energy depends on its frequency – red photons have less energy than violet photons • Dual Theory of Light: Light moves through space as a wave and interacts with matter as a particle

18. Production of Light • Illuminated objects = reflect light, ex. Moon • Luminous objects = emit light, ex. Sun • Different methods to produce light based on how they excite electrons: • Heating gases • Heating metal filaments • Electricity • Ultraviolet radiation • Chemoluminescence • Bioluminescence • Phosphorescence

19. Polarization of Light • Only occurs with transverse waves • Polarized materials have molecules that only allow EM waves of one direction pass through them = polarizing axis • Blocks waves perpendicular to polarizing axis • Example, polarized sunglasses reduce glare of light reflecting off a variety of surfaces