Chapter 16 – Light

What type of wave is light?(last chapter)

ELECTROMAGNETIC SPECTRUM• Contains only transverse waves• All forms of light are included• EM spectrum usually shown from low

frequency to high frequency– this also means that the wavelength goes

from long to short on the same scale• No medium is required for these waves to

travel

Radio wave

Micro wave

Infrared (IR)

Visible

ROYGBIV

Ultraviolet (UV)

X-wave Gamma wave

Communication (radio, cell phone, satellite)

Communication

Heat food

Remote control

Thermal imaging

What we see “black light”

Sun

X-ray Large stars

Nuclear reaction

EM Spectrum

“KINDA NEW” EQUATION

c = c : speed of light

(3x108 m/s)

: wavelength (m)

: frequency (Hz)

Types of Materials• Opaque:

– material absorbs/reflects all of the light– no light gets through (ex. Brick)

• Translucent:– material absorbs/reflects some of the light– most light gets through (ex.lamp shade)

• Transparent:– material absorbs/reflects none of the light– all light passes through (ex. glass)

Confusing Vocabulary

• Luminous: an object that emits light• Illuminated: an object that reflects light• Luminous flux []: the rate at which light

is emitted• Lumens (lm): the unit for luminous flux• Illuminance [E]: the amount of light

incident on a surface• Lux (lx): the unit for illuminance

Illuminance Equation

E =

4 r2

where:E is illuminance (lux)

is luminous flux (lumens)

r is the distance from the source (meters)

Producing LightIncandescent– A piece of metal in

a closed space is heated by electricity

– Filament (glowing metal) made of tungsten

Fluorescent– An electric current

is sent through a gas (mercury and argon) in a closed space

– Similar to lightning

All artificial producers of light follow one of these two methods. The only exception is a laser.

COLORS & PIGMENTS OF LIGHT

• Additive color process – all three colors of light have the correct intensities, they appear white.

• Primary colors:.– red

– green

– blue

• Primary Pigments – absorbs only one primary color and reflects two from white light.

– yellow (absorbs blue, reflects red and green)

• Secondary pigments – absorbs two primary colors and reflects one (red, green., and blue)

Polarization

• Light is a transverse wave that oscillates in more than one direction

• Polarization is when light is forced to choose one particular direction of oscillation (light coming off of a road is reflected and becomes polarized).

• Ex. – polarized sunglasses – keeps the glare off

• Types:

– Vertical and horizontal (most common)

– Clockwise and counterclockwise

Ch 16 Homework

53. 2 lux54. 3.84x108 m55. 100 Watts57. 1306 lm58. 15,000 km

59. 7.0x10-7 m62. Vertically65. 2.3 m67. 14.7 m68. light takes 5 s,

while sound takes 4.7 s