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

• 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