Transcript Electromagnetic Waves - Grosse Pointe Public School System

Electromagnetic Waves
An electromagnetic wave has both
an electric
and magnetic component associated with it.
Unlike mechanical waves, electromagnetic
waves can travel through a region void of
matter and mechanical waves cannot.
In other words…. EM waves do not need
a medium
Electromagnetic Waves
Complete the diagram by labeling the following
regions:
ultraviolet, infrared, x-ray, radio & TV, gamma, and
microwave.
infrared
Visible
Light
x-ray
gamma
c  f
Electromagnetic Waves
1. Which region of the electromagnetic spectrum
has the highest frequency?
Gamma rays
2. Which region of the electromagnetic spectrum
has the longest wavelength?
Radio/TV
3. Which region of the electromagnetic spectrum
will travel with the fastest speed?
ALL THE SAME SPEED…. The
Speed of light The speed of light, 299 792 458 m / s
c  f
Or
c = 300,000,000 m/sec
3 x 108 m/sec WRITE THIS DOWN!
Electromagnetic Waves
It is known that electromagnetic waves with
longer wavelengths have a greater ability to
bend around obstacles that get in their path.
This ability to bend around obstacles is referred
to as diffraction.
Electromagnetic waves with strong diffraction
properties are used in communication.
4. Which two regions of the spectrum have the
greatest ability to diffract?
Radio and microwaves longest wavelength
Electromagnetic Waves
It is known that electromagnetic waves with high
frequency are more capable of causing damage
to the organs of living things.
5. Which two regions of the spectrum have the
tendency to cause the greatest damage to
humans?
Gamma and x-ray
Electromagnetic Waves
• Radio Waves
– AM
Amplitude Modulated
• 500-1500 kHz
• 600 - 200 m
– FM
• Television
– Old Channels
• VHF = 108-122 MHz
• UHF =470-890 MHz
Frequency Modulated
• 54-1600 MHz
• 5.55 m - 0.187 m
– XM/Sirius Satellite
• 2.3 GHz
– New Digital Channels
• Many materials transmit light, meaning allow light to
pass through it.
• We call these materials a medium (plural: media)
• Every medium for light has what is known as an “index
of refraction”
• It is just the ratio of how fast light should go, to how
fast it does go in a medium
• Its symbol is “n”
• It’s just a number greater than 1
Introductory Terms
•
measure
• We
A ray
of lightthose
strikes
angles
NOTWe
from
a surface.
callthe
surface,
from
that ray rather
an
a
“NORMAL”RAY.”
line
“INCIDENT
•
• Normal
That raymeaning
reflects off
perpendicular
tothe
the
of the surface at
surface
same angle as the
incident ray
i  r
i
r
ReFLEction & ReFRAction
• When
The angle
“incident”
of incidence
light
• When light changes
strikes
and
theaangle
medium
of such
direction- that’s
as water, glass,
refraction
are or
REFRACTION.
some goopy
governed
byliquid,
what is
some light
called
Snell’s
reflects
Law off
of the surface.
i
i part
 n rofsin
•n
The
other
the r
i sin
goes of
into
the
• light
ni – index
refraction
for
medium.
incident ray
• When
it does,
the
nr – index
of refraction
for
medium
refractedcan
rayactually
down
light,
 slow
qi – angle
ofthe
incidence
causing a change in
 qr – angle of refraction
direction.
r


Total Internal Reflection
• Occurs when incident light completely reflects- no refraction into the
next medium
• Light can refract out, say from glass to air
• At a certain angle of incidence, the refracted angle is 90o. We call that the
“Critical Angle”
• Total Internal Reflection is what makes Fiber Optic Communication
possible.
• Can only occur when ni > nr
r
Air
Glass
i i