electromagnetic waves. electromagnetic waves- transverse waves consisting of changing electric...
TRANSCRIPT
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