Transcript EM Spectrum - Cobb Learning

Light is a WAVE
Electromagnetic Spectrum and
EM Waves
EM Waves
• Light is part of the ELECTROMAGNETIC
SPECTRUM
• EM WAVES are radiated by ALL objects at
the SPEED OF LIGHT
• c = 3 x 108 m/s (in vacuum)
Example
v = fλ #1
What is the wavelength
of a radio
wave traveling
8
4
3 x 10 m/s = (5 x 10 Hz) λ
through outer space with a frequency of 5 x 104 Hz?
λ = 600 m
EM Wave Production
Changing electric fields
produce MAGNETIC FIELDS
Changing magnetic fields
produce ELECTRIC FIELDS
The result is a selfpropagating wave with
perpendicular ELECTRIC
and MAGNETIC fields
These waves DO NOT
REQUIRE A MEDIUM
EM Wave Speed
• Depends on the
Example
medium
#2
What is the speed of light in lucite?
c

• The “speed” ofn
anmedium
depends
on
its
= 1.50
density and is described
by its INDEX OF
v
REFRACTION (n)
n=c/v
Index of Refraction
= speed
light
1.50 = (3
x 108 of
m/s)
/ vin vacuum
speed
of light
in faster
medium
• The closer the index
is to
1, the
the
medium
v = 2 x 108 m/s
Wein’s
Law
EM
Waves
ALL objects emit EM radiation with a frequency directly
related to their temperature
Outer space  3K
Humans  310K
Sun  5630K
Example #3
• Red light has a wavelength of
about 750 nm. Violet light has
a wavelength of about 400 nm.
Betelguese
– Which color of light is emitted
with a higher frequency?
• Shorter wavelength = higher
frequency, so violet is higher
– Which star is hotter, Betelgeuse
or Rigel? How can you tell?
• Wein’s Law says that hotter
objects emit HIGHER
frequencies, so blue stars are
hotter – red ones are cooler
Rigel
EM Waves Summary
• EM waves travel at THE SPEED OF LIGHT.
– That speed depends on the MEDIUM OF TRAVEL
• EM waves do not require a MEDIUM.
• Low frequency EM waves (below ultra violet) are
NON-IONIZING forms of radiation
• High frequency EM waves (ultra violet and
higher) are IONIZING forms of radiation
– Dangerous to life  mutations, cancer, etc.