Download Chapter 5: Light and Quantized Energy - Ms. McDonald

Light’s Wave Nature
Wave Nature of Light
• Electromagnetic radiation is a form of
energy that exhibits wavelike behavior as
it travels through space.
• Examples: sunlight, microwaves, x-rays
radio and television waves
Characteristics of Waves
• Wavelength (λ – lambda) – the shortest distance between the
same points on a wave; usually measure in meters, centimeters, or
nanometers
• Frequency (f)– the number of waves that pass a given point per
second; 1 Hertz equals 1 wave per second (1/s or s-1)
• Amplitude is a waves height from origin to crest
Speed of Light
• All electromagnetic waves travel at the
speed of light in a vacuum and this value
is a very important constant
c = 3.00 x 108 meters per second (m/s)
• The speed of light is related to wavelength
and frequency by the following equation:
c = wavelength x frequency
or
c=λf
Using the Equation
• c=λf
• Looking at the
equation, you
can see that
wavelength and
frequency are
inversely
related, so as
one increases
the other
decreases and
vice versa.
Light and the Visible Spectrum
• Sunlight or white light is made up of a
continuous range of wavelengths and
frequencies.
• Passing sunlight through a prism show
you all the color of the visible spectrum
• When passing through a prism, the short
wavelengths bend more than the
long ones, resulting in the
sequence of colors
» ROY G BIV (red, orange, yellow, green, blue, indigo,
violet)
Electromagnetic Spectrum
Includes all forms of electromagnetic radiation, with the
only difference being wavelength and frequency
Calculations
• Because all electromagnetic radiation
travels at the same speed (speed of light),
we can use the formula c = λ f to
calculate wavelength and frequency any
wave. Remember c = speed of light!
Quantum?
• A quantum is the minimum amount of
energy that can be gained or lost by an
atom; so matter can gain or lose energy
only in small, specific amounts.
• So how does that relate to energy
levels in an atom?
Ground State vs. Excited State
The ground state of an electron is the
lowest energy level possible for that
electron. It’s comfortable there. By
adding energy, like heat or light,
electrons can be exited and move up to
a new energy level – they would then be
in an “excited state”.
This “excited state” is very
uncomfortable for the electron, it wants
to be back home in its ground state
energy level, so it loses the energy it
gained (the quantized amount) and
begins to drop back down to its lowest
energy level (kind of like stepping down
a ladder).
Sometimes the energy it loses can be
seen as colors of light because the
frequency of the energy is in the “visible
light” range.”
Photons
• A photon is a particle of electromagnetic
radiation (like visible light) with no mass that
carries a quantum of energy. So basically, it’s a
package of electromagnetic radiation with a set
amount of energy.
• Photons can travel at different wavelengths and
frequencies, so we interpret that as different
colors of light. (remember, visible light can have
different wavelengths and frequencies that we
see as different colors!)
Bohr’s Model
• We can use this equation to relate the
amount of quantum energy to the actual
frequency of the radiation.
E = hf
E is the quantum energy or a photon’s energy, h is
Planck’s constant (6.626 x 10-34 J · s), f is the
frequency
Practice
1. What is the energy for the following type
of radiation?
6.32 x 1020 s-1
2. Use the Electromagnetic Spectrum to
determine the type of radiation described
in problem #1.