1. Electromagnetic Spectrum
LIGHT
Principles of Physics

2. 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

4. 5.20x1014 Hz
3.84x1014 Hz
4.82x1014 Hz
5.03x1014 Hz
6.10x1014 Hz
6.59x1014 Hz
7.69x1014 Hz
Red Orange Yellow Green Blue Violet

6. 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

7. 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

8. Visible Light Waves that allow us to see color
Red – longest wavelength, lowest frequency
(3.84 x Hz = 384,000,000,000,000 Hz)
Violet – smallest wavelength, highest frequency (7.69 x 1014 Hz = 769,000,000,000,000 Hz)

9. 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?

10. Characteristics of Light Waves
Intensity (brightness) = amplitude
Large amplitude, a lot of energy (very hot)
Small amplitude, less energy (warm)

11. 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

12. 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)

13. Speed of light in a vacuum = c = 299,792,458 m/s
= 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 / ≈ 3.00 x 108 m/s
Water c/1.33
Diamond c/2.42

14. Scientific Notation
Put a decimal after the first non-zero number and drop any zeroes
Determine the power of ten by counting the places before of after the decimal
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
→ 3.45
2. Ex: 300,000,000 → places after
→ 3.45
4 places before
Ex: 300,000,000 →
3.0 x108 →
3.45 x 10-4