Transcript Light and the Electromagnetic Spectrum

Light
and the
Electromagnetic
Spectrum
The Electromagnetic Spectrum
The electromagnetic spectrum represents
the range of energy from low energy, low
frequency radio waves with long
wavelengths up to high energy, high
frequency gamma waves with small
wavelengths.
Visible light is a small portion of this
spectrum. This is the only part of this
energy range that our eyes can
detect. What we see is a rainbow of
colors.
RedOrangeYellowGreenBlueIndigoViolet
ROY G BIV
Frequency Ranges of Visible Light
Red light has a frequency of roughly
4.3 × 1014 Hz, and a wavelength of about
7.0 × 107 m (700nm).
Violet light, at the other end of the visible
range, has nearly double the
frequency—7.5 × 1014 Hz—and (since
the speed of light is the same in either
case) just over half the wavelength—
4.0 × 107 m (400nm).
The radiation to which our eyes are
most sensitive has a wavelength near
the middle of this range, at about
5.5 x 10-7m (550 nm), in the yellowgreen region of the spectrum.
C = λν
• The frequency (v) of a wave is
the number of waves to cross a
point in 1 second (units are Hertz –
cycles/sec or sec-1)
• λ is the wavelength- the distance
from crest to crest on a wave
• The product of wavelength and
frequency always equals the
speed of light.
C = λν
• Why does this make sense?
• NOTE:
c is a constant value= 3.00 x 108 m/s
PROBLEMS
• Calculate the wavelength of yellow light
emitted from a sodium lamp if the
frequency is
5.10 x 1014 Hz (5.10 x 1014 s-1)
List the known info List the unknown
c = 3.00 x 1010 cm/s
wavelength (λ) = ? cm
Frequency (v) = 5.10 x 1014 s-1
C = λv
λ=c
v
λ = 3.00 x 1010 cm/s = 5.88 x 10-5 cm
5.10 x 1014 s-1
YOUR TURN
1- What is the wavelength of radiation
with a frequency of 1.50 x 1013 s-1?
2- What
frequency is radiation with a
wavelength of 5.00 x 10-6 cm? In what
region of the electromagnetic
spectrum is this radiation?
Flame Test
Debrief
© 2000 Microsoft Clip Gallery
• Light Energy
– Atoms
• As atoms absorb energy, electrons jump out to a
higher energy level.
• Electrons release light when falling down to the lower
energy level.
– Photons - bundles/packets of energy released
when the electrons fall.
• Light: Stream of Photons
© 2000 Microsoft Clip Gallery
Ground state of an
electron is the energy
level it normally occupies
When an electron
temporarily occupies an
energy state greater than
its ground state, it is in an
excited state
An electron can become
excited if it is given extra
energy – absorbing a
photon – packet of light
Electrons do not
stay in excited
states very long.
Electrons return to
the ground state,
but emit a photon
when it does so.
Transverse
Waves
© 2000 Microsoft Clip Gallery
• Energy is perpendicular to direction
of motion
• Moving photon creates electric &
magnetic field
–Light has BOTH Electric &
Magnetic fields at right angles!