LIGHTChapter 14

What is Light?

A wave Carries energy (heat) Has color Different l and f Can be reflected and refracted Shows destructive interference

Is a particle Travels without a medium (space)

Is both a wave and a particle Acts like a wave and a particle Considered a photon (a packet or unit of light)

Transverse wave on 2 planes of motion 1. electric field (on vertical plane) 2. magnetic field (on horizontal plane)

How is light made?

Atoms Have a nucleus with p+ and n0

Orbiting around are e-

Farther e- are from the nucleus, the more energy they have Move towards nucleus, they lose energy

(give off light)

Examples

Light bulbs1. Incandescence - making light with

heat Filament inside is heated e- in filament gain and lose energy,

which gives off light Give off A LOT of heat, wastes energy

2. Fluorescent - add energy to e-

inside a gas Little heat created, so little is lost

Examples of Light

Glow in the dark objects Photoluminescence – process of

creating light Objects contain Phosphorus Exposed to any light, e- gain energy Lose energy very slowly Once energy is gone, it can be

“recharged” by putting it back in the light

The Speed of Light (“c”)

The “universal speed limit” – nothing in universe can go faster than light Unaffected by any medium Is 3 x 108 m/s (300,000,000 m/s)

Can circle the Earth 7.5 times in 1 sec Light from the sun is 8 seconds old

We use light to determine distance in space:

1 light year = the distance light travels in one year

What can we see?

We see white light Separate white light with a prism

Prisms use refraction

Get different colors (ROY G BIV) Also called visible light

Colors have different energies (f & l) Think about fire –

red flames are coolest blue are hottest

As you move from red to blue: light GAINS energy, so shorter l

White light is hottest since made up of all colors

Color can also tell us other things: We can determine their chemical make-up

based on the colors we see (i.e. stars)

Visible and Invisible Light

The amount of energy given off by e- varies greatly Leads to different l Small l are measured in nanometers

(nm) 1 nm = 1 x 10-9 m

Whole range of energy is known as the Electromagnetic radiation (EMR) All light in this spectrum travels at (c)

EMR Organized longest l to shortest l Longer l = low energy, low frequency Shorter l = high energy, high frequency

DANGEROUS STUFF!

1. Radio waves: very high l, low energy waves Used to transmit radio and TV signals

Radio towers are so tall – to make long radio waves

2. Microwaves: Used to cook food (by vibrating water

molecules) Cell phones transmissions

3. Infrared: Shows heat signatures of

objects

4. Visible Light: What we see – colors

5. Ultraviolet Light (UV): Causes sunburns and skin cancer Much of this is absorbed by the ozone layer

6. X-Rays: Small enough l to penetrate materials and

tissues Medical use: see bones or teeth

7. Gamma Rays: most powerful & most dangerous Lowest l & highest energy Emitted from nuclear reactions Can break cellular bonds and cause

mutations (cancer) Medical use: used to help treat cancer