Chapter 14

Electromagnetic Waves: Light  A light wave is a transverse wave that consists of electric and magnetic field waves at right angles to each other.  Light has a dual nature in which it exhibits behaviors that are characteristic of both waves and particles.

Light comes in a wide range of frequencies and wavelengths.

Electromagnetic Waves  Electromagnetic waves are waves caused by a disturbance in electric and magnetic fields and that do not require a medium; also called a light wave.  Visible light is only one part of the electro- magnetic spectrum

Wave Interference  Interference is the combination of two or more waves that exist in the same place at the same time.  Two different material objects can never occupy the same space at the same time.  Waves, however, can pass through one another.  When this happens, the waves form an interference pattern. This ripple tank demonstrates the interference of water waves.

Interference of Light waves  Interference of light waves creates colorful displays.  You can see a rainbow of colors when oil is spilled onto a watery surface.  These colors are due to interference of light. Spilt oil on watery asphalt

Diffraction  Diffraction is the bending of a wave as it passes an edge or an opening.  When waves pass the edge of an object or pass through an opening, such as a door, they spread out as if a new wave were created there.

Light Brightness  The farther you are from a light source, the light spreads out in all directions and appears less bright.  The brightness of light decreases by the square of the distance from the source.

Light has a finite speed  All electromagnetic waves in empty space travel at the same speed, the speed of light, which is 3x10 8 m/s.  Light travels slower when it has to pass through a medium such as air or water.

Reflection of Light  The texture of a surface affects how it reflects light.  Diffuse reflection  Specular reflection  Incoming and reflected angles are equal : Law of Reflection

Color and Polarization

Color  The color of an object depends on which wavelengths of light shine on the object and which wavelengths are reflected. Figure A leaf appears green under white light because the pigment in the leaf reflects only green light.

Additive Primary Colors  Red, green and blue are additive primary colors because when they are added to varying proportions they can form all of the colors of the spectrum.

Subtractive Primary Colors  The primary subtractive colors are cyan, magenta, and yellow.  When any two primary subtractive colors are combined, they produce either red, green or blue pigments.

Polarization of Light Waves  Light waves that have electric fields oscillating in random directions are called unpolarized.  Light can be linearly polarized by transparent crystals.

Polarization of Light by Transmission, Reflection, and Scattering