Let there be light What is light Energy
Let there be light
What is light? • Energy carrying waves emitted by vibrating electric charges in atoms – When electrons in the outer shell of an atom jump to different energy levels, they get excited and produce light. – Photons are produced when this occurs • There are forms of “light” we can not see. Which ones?
• Light travels VERY FAST – around 300, 000 km/s = c. At this speed it can go around the world 7. 5 times in one second. • 3 x 108 m/s or 186, 000 miles/second c = fλ
How long does it take light to travel…. • • • One mile? 5. 3 x 10 -6 sec From NY to LA? 0. 016 sec Around the equator of the Earth? 0. 133 s From the moon to the Earth? 1. 29 s From the sun to the Earth? 8 minutes From Alpha Centuri 4 years
Properties of Light • Light appears to travel in straight lines: Laser • • Can carry heat Has color Can be bright or dim Travels almost unimaginably fast • Can be bent by lenses or reflected by mirrors
Important Properties of Light • Amplitude determines brightness • The greater the amplitude, the greater the brightness • Wavelength determines color • Light is made of photons, which have properties of both particles and waves
Ma Light Pigment Red low l e Y ge nta Pu White Blue Cyan e ng a r O rpl e Black Green Blue Green Yellow
Mixing Colors of Light
Electromagnetic Spectrum f=~1015 Hz f=~1012 Hz f=~108 Hz f=~104 Hz f=~1016 Hz f=~1018 Hz f=~1020 Hz The greater the frequency the smaller the wavelength The greater the frequency the greater the energy The greater the energy, the more dangerous (cancer)
Light and Materials • Transparent materials= allows light to pass through them – Light hits them, their atoms absorb the energy and release it quickly – Light slows down when passing through transparent material • Water transmits light at 0. 75 c • Glass 0. 67 c • Diamond 0. 41 c
Transparent Materials • object through which light can pass in straight lines http: //www. gcsescience. com/pwav 21. htm
Opaque Materials • absorb light without re-emission and so no light goes through them • The absorbed light is transformed into kinetic energy and heat
Translucent Material • Allows some light to pass through • ex: a filter or tinted glass http: //www. ronbigelow. com/articles/color-perception-2/perception-2 -6. jpg
Why is a strawberry red?
Day 2
Mirrors • Mirrors are any shiny smooth surface • Three types of mirrors – convex, concave, and plane
Mirror Images • Real Image • Image that is formed by converging light rays that can be displayed onto a screen. • EX: rays of light from an overhead projector • Virtual Image • Image formed through reflection or refraction. • Can be seen by the observer, but cannot be projected onto a screen • EX: plane mirror image
Plane mirrors • Flat surface • produces a virtual image that is upright and reversed and same size mirror NOT REAL VIRTUAL IMAGE
Concave vs. Convex
Convex Mirror • curves outwards in the middle • produces an image that is virtual, upright and smaller than the object Reflected light rays never meet so they cannot produce a real image
Convex Mirror
Concave Mirror • curves inward and forms a virtual or real image (upside down image formed when rays actually meet at a point)
Concave Mirror: object is beyond focal point http: //sol. sci. uop. edu/~jfalward/reflection 55. html
Object (girl’s face) is between focal point and mirror http: //sol. sci. uop. edu/~jfalward/reflection 55. html
Lenses - Refraction • There two types of lenses Concave and Convex • Lenses work because of refraction
Concave (Diverging) lenses • Produces a virtual image- refracted light rays do not cross • A lens that is thinner in the middle than at the edges.
Convex (Converging) lenses • Produces a real image- refracted light rays do cross at the focal point • A lens that is thicker in the middle than at the edges.
- Slides: 29