Electromagnetic Waves

Electromagnetic Waves- transverse waves consisting of changing electric fields and changing magnetic fields Electric Field- a region of space exerts electric forces on charged particles Magnetic Field- a region of space produces magnetic forces

If one changes the other changes so they regenerate each other Electromagnetic waves are produced when an electric charge vibrates or accelerates

Electromagnetic waves can travel though a vacuum, or empty space, as well as through matter!

Electromagnetic radiation- transfer of energy by electromagnetic waves traveling through matter or across space

Thunder and Lightning

Speed of Light Albert Michelson (1852-1931)- American physicist who first measured the accurate speed of light.

All electromagnetic waves travel at 3.00x108 m/s

The only difference in electromagnetic waves is their wavelength and frequency Remember: v=λf

Wave or Particle? Electromagnetic radiation behaves sometimes like a wave and sometimes like a stream of particles.

Evidence for the Wave Model Thomas Young (1773-1829)- English physicist

Evidence for the Particle Model Albert Einstein (1879-1955) Proposed that light, and all electromagnetic radiation, consists of packets of energy called photons Photoelectric effect- emission of electrons from a metal caused by light striking the metal

Intensity Intensity- the rate at which a wave’s energy flows through a given unit of area The intensity of light decreases as photons travel farther from the source.

Wavelength Range Frequency Range Common Uses Interesting Information

Behavior of Light Light and Materials Materials can be transparent, translucent, or opaque

Transparent A material through which you can see clearly; transmits light, which means it allows most of the light that strikes it to pass through

Translucent A material that scatters light; makes objects look fuzzy or unclear

Opaque Either absorbs or reflects all of the light that strikes it; you cannot see through these objects

Interactions of Light When light strikes a new medium, the light can be reflected, absorbed, or transmitted. When light is transmitted, it can be reflected, polarized, or scattered

Reflection Image- a copy of an object formed by reflected (or refracted) waves of light Regular reflection- occurs when parallel light waves strike a surface and reflect all in the same direction (smooth polished surface) Diffuse reflection- when parallel light waves strike a rough, uneven surface, and reflect in many different directions

Refraction Bending of waves as it passes through a new medium Mirage- a false or distorted image caused by hotter air above the surface refracting light waves; often looks like water

Polarization Polarized light- light with waves that vibrate in only one plane Polarized sunglasses have vertical polarized filters so that horizontal polarized light is blocked reducing glare

Scattering- light is redirected as it passes through a medium

COLOR

Separating White Light Into Colors White sunlight is made up of all the colors of the visible spectrum As white light passes through a prism, shorter wavelengths refract more than longer wavelengths and the colors separate Dispersion- process in which white light separates into colors Red- longest wavelength- least bent Violet- shortest wavelength- bent most

Double Rainbow

The Colors of Objects The color of any object depends on what the object is made of and on the color of light that strikes the object. Pigment- material that absorbs some color of light and reflects others Photography Link

Secondary Colors- Combination of 2 primary colors Primary Colors- 3 specific colors that can be combined in varying amounts to create all possible colors In Light: Red, Green, and Blue In Pigment: Cyan, Magenta, and Yellow Secondary Colors- Combination of 2 primary colors In Light: Cyan, Magenta, and Yellow In Pigment: Red, Green, and Blue

Complimentary Colors In Light: Any two colors that combine to make white In Pigment: Any two colors that combine to make black

The Law of Reflection Ray diagram- shows how rays changed direction when they strike mirrors and pass through lenses.

Virtual image- a copy of an object formed at a location from which light rays appear to come Remember: rays do not actually come from behind the mirror!

Concave Mirrors Concave Mirrors- when the inside surface of a curved mirror is the reflecting surface Focal point- the point at which the light rays meet Real image- a copy of an object formed at the point where light rays actually meet Can be viewed on a surface such as a screen Concave mirrors can form either real or virtual images When the object is farther from the mirror than the focal point, the reflected rays meet in front of the mirror When the object is closer to the mirror than the focal point the reflected rays spread out and appear to come from behind the mirror

Convex Mirrors Convex mirrors- when the outside surface of a curved mirror is the reflecting surface Convex mirrors always cause light rays to spread out and can only form virtual images

Lenses Light travels at 3.00 x 108 m/s in a vacuum. As it passes through new media it slows down Air- almost 3.00 x 108 Water- 2.25 x 108 Glass- 2.00 x 108

When light enters a new medium at an angle, the change in speed causes the light to bend or refract

Lens- Object made of transparent material that has one or two curved surfaces that can refract light Concave lens- curved inward at the center and is thickest at the outside edges Concave lenses always cause light rays to spread out and can only form smaller virtual images Convex lens- curved outward at the center and is thinnest at the outer edge Convex lenses form either real or virtual images

Convex lens Concave lens