1. Light Physics Ms. Johnson

2. Early Concepts Most philosophers and scientists believed light consisted of particles Christian Huygens was the first to argue that light was a wave In 1905, Einstein published a paper on the photoelectric effect, where he explained light consisted of particles called photons Scientists now agree that light has a dual nature, as a particle and as a wave

3. Speed of Light Several different measurements –Pre - 17th century –Galileo –Olaus Roemer 1676 –Michelson (1926) Represented by the symbol c =3.0x10^8 m/s Light-year - distance light travels in one year

4. Electromagnetic Waves Light is energy that is emitted by accelerating electric charges This is called an electromagnetic wave This is a transverse wave This wave type includes radio waves, microwaves, x-rays which are all part of the electromagnetic spectrum Visible light has a wavelength from 400nm – 700nm Red light has the lowest frequency Violet has the highest. Waves with a frequency lower than red light are infrared Waves with frequencies higher than violet are ultraviolet

5. Types of Electromagnetic Waves

6. Transparent & Opaque Transparent materials allow light to pass through them Light can slow down as it passes through these materials –Ex: glass-.67c water -.75c Opaque materials allow no light to pass through them. A material can be transparent to some wavelengths and opaque to others

7. Shadows A thin beam of light is called a ray. Any beam of light can be thought of as a bundle of rays When a beam of light shines on an object, some of the rays may be stopped while others may continue on their straight-line path A shadow is formed where light rays cannot reach. A total shadow is called an umbra A partial shadow is called a penumbra - it occurs when some light is blocked but other light fills in

8. Eclipse An eclipse is an example of a shadow When the moon is between the sun and Earth it casts a shadow –The darkest part of the shadow is the umbra –The lighter, outer part is the penumbra There are 2 types of eclipses, solar and lunar

9. Lunar vs. Solar Eclipse

10. Polarization Light travels in transverse waves that go out in all directions When waves are polarized, they are only allowed to travel in one direction Filters can be used to create polarized light If two polarizing filters are placed at 90° to each other, no light will get through.

11. Polarized Glasses

12. 3D Viewing Seeing in 3 dimensions depends on both eyes giving the same impressions simultaneously. A pair of photos placed a short distance apart This can be done in slide shows or movies by projecting 2 polarized pictures on the same screen and viewing it through 2 different polarized lenses