Electromagnetic Waves Phys Sci 1-19-12

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16 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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Electromagnetic Waves

Phys Sci 1
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19
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12


What is an Electromagnetic Wave?


Some waves do not need a medium to transfer energy. These are electromagnetic waves. You are
surrounded by plenty of these all the time: radio waves, infrared waves, visible light,
ultraviolet
rays, and maybe even small amounts of X
-
rays or gamma rays.



Electromagnetic wave
: a transverse wave that transfers

electrical and magnetic
energy


An electromagnetic wave consists of vibrating electric and magnetic fields that move through
s
pace at the speed of light. These fields are found at right angles to each other.


















P
roducing Electromagnetic Waves

Light and all other electromagnetic waves are produced by charged particles. Every charged
particle has an electric field
surrounding it. The electric field produces electric forces that can
push or pull on other charges particles.


When a charged particle moves, it produces a magnetic field. This can affect materials around it.


Magnetic field
: a region of

space near a charged particle
or magnet that exerts magnetic
forces that can act on

certain materials


When a charged particle changes its motion, its magnetic field will change in relation
--

and vice
versa. When one field vibrates so does the other. In
this way, the two fields are constantly
causing each other to change. The result is an electromagnetic wave.



Energy

Electromagnetic waves do not require a medium, so they can transfer energy through a vacuum.
This is how you can see the light from the su
n and stars
--

it reaches Earth through the empty
vacuum of space.



Vacuum
: a space entirely devoid of matter


Electromagnetic radiation
: the energy that is transferred through space by
electromagnetic waves


Speed

All electromagnetic waves travel at the s
ame speed in a vacuum. The speed of light is about
300,000 kilometers per second (about 186,000 miles per second). At this speed, light from the
sun takes about 8 minutes to travel the 150 million kilometers to Earth. When light travels
through a medium su
ch as air, they travel more slowly, but the speed of light waves in air is still
about a million times faster than the speed of sound waves in air.



Speed of light
: the distance light can travel in a unit of time through a given substance


Models of Elect
romagnetic Waves


Many properties of electromagnetic waves can be explained by a wave model. However, some
properties are best explained by a particle model. It may be difficult for you to picture
electromagnetic waves, like light, as being both waves and
particles at the same time
--

but both
models are necessary to explain all the properties of light.


Wave Model of Light

The lenses of many sunglasses are polarizing filters. Light acts as a wave when it passes through
a polarizing filter. Ordinary light ha
s waves that vibrate in all directions. A polarizing filter acts
as though it has it has tiny slits that are aligned in only one direction meaning only some light
will pass through a polarizing filter.


Polarizing filter
: a filter tha
t only allows light wa
ves that
vibrate in one direction to travel
through



Polarized light
: the light tha
t travels through a filter and
vibrates in only one direction











Particle Model of Light

Sometimes light behaves more light a stream of particles. When a bean of li
ght shines on some
substances, it cause tiny particles called electrons to move. The movement of electrons causes an
electric current to flow. Sometimes, light can even cause an electron to move so much that it is
knocked out of the substance.


Photoelectr
ic effect
: the emission, or ejection, of electrons

from a material as a result of
being struck by
electromagnetic radiation


The photoelectric effect can be explained only by thinking of light as a stream of particles
--

tiny
packets of energy
--

all moving

toward that substance. Albert Einstein first explained the science
behind the photoelectric effect in 1905.



Photon
: a unit of electromagnetic radiation