ELECTROMAGNETIC SPECTRUM

LIGHT

Principles of Physics

Electromagnetic Spectrum Waves created by fluctuating electric and

magnetic fields

Transverse waves Can travel in a vacuum – do not need a medium Travel at the speed of light in a vacuum

(c = 300,000,000 m/s) Organized by frequency and wavelength

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35

3.84

x1014

Hz

4.82

x1014

Hz

5.03

x1014

Hz

5.20

x1014

Hz

6.10

x1014

Hz

6.59

x1014

Hz

7.69

x1014

Hz

Red Orange Yellow Green Blue Violet

Radio, Micro, and Infrared Waves

Longest wavelength and lowest frequency

RADIO WAVES ARE NOT SOUND WAVES

Provide the signal for communications devices such as: radios, television, cell phones

Micro waves are used to cook food Infrared waves are used for TV remote

controls, night vision

Ultraviolet, X and Gamma Waves

Shortest wavelength, highest frequency Cause damage to human cells because

wavelength is close to atomic size Ultraviolet – sun bathing X – used to detect bone damage,

baggage screening at airports Gamma – radioactive decay

Visible Light

Waves that allow us to see color Red – longest wavelength, lowest frequency

(3.84 x 1014 Hz = 384,000,000,000,000 Hz) Violet – smallest wavelength, highest

frequency (7.69 x 1014 Hz = 769,000,000,000,000 Hz)

Light Sources Emit light waves Produce light Sun, light bulbs, flames

Illuminated Objects Most objects Actually are reflecting light People, plants, rocks, etc.

Moon – source or illuminated?

Characteristics of Light Waves

Intensity (brightness) = amplitude

Large amplitude, a lot of energy (very hot)

Small amplitude, less energy (warm)

Characteristics of Light Waves Color = frequency

Order of colors = spectrum Primary colors of light – red, green and blue

Red light +green light +blue light = white light Different than pigment colors (ink, paint, etc)

These reflect light, they are not sources

Mixing colors Applet

Light can be reflected or transmitted:

Materials Transparent – transmit

clearly (clear glass, still water)

Translucent – transmit blurry (frosted glass)

Opaque – no transmission (light may be reflected or absorbed)

Speed of light in a vacuum = c = 299,792,458 m/s

= 2.99792458 x 108 m/s ≈ 3.00 x 108 m/s

Speed of light in any other material depends on optical density (ability of a material to transmit light) Greater optical density, more light slows down

Air c / 1.003 ≈ 3.00 x 108 m/s Water c/1.33Diamond c/2.42

Scientific Notation1. Put a decimal after the first

non-zero number and drop any zeroes

2. Determine the power of ten by counting the places before of after the decimal

3. Show the places before or after the decimal using an exponent. Use a negative on your exponent if the decimal is before the number

1. Ex: 300,000,000 → 3.0

0.000345 → 3.45

2. Ex: 300,000,000 → 3.0 8 places after

0.000345 → 3.45

4 places before 3. Ex: 300,000,000

→ 3.0 x108

0.000345 → 3.45 x 10-4