Transcript SC3 (f): Relate light emission and the movement of electrons to

Dual Wave-Particle Nature of Light
Essential Question(s):
Standard(s):
SC3 (f): Relate light
emission and the
movement of electrons
to element
identification
1. What is the relationship
between the wavelength,
frequency, and energy of
light?
2. How can the dual waveparticle nature of light be
used to understand the
dual wave-particle nature
of electrons in atoms?
Performance Tasks:
• Discuss the dual wave-particle nature of light and relate
it to the electron.
• Calculate the mathematical relationship among the
speed, wavelength, and frequency of electromagnetic
radiation
A. Rutherford’s Atom
Electromagnetic Radiation
• Energy travels through space by electromagnetic
radiation
–
–
–
–
Gama Rays
Ultraviolet
Infrared
Radio wave
X-rays
Visible Light
Microwaves
• The different forms of electromagnetic radiation
exhibit the same type of wavelike behavior and
travel at the speed of light in a vacuum.
B. Energy and Light
• Electromagnetic radiation
Waves have 3 primary characteristics
– Wavelength = lambda ()= distance between 2
consecutive peaks or troughs
– Frequency = nu () = number of waves (cycles)
per second that pass a given point in space
– Since all waves travel at the speed of light, short
wavelength radiation must have a high frequency.
=c
C = speed of light (2.9979*108m/s)
 And  are inversely proportional
Units
• Wavelength =
lambda ()= meters
• Frequency = nu () =
s-1 or hertz
The
Nature of
Waves
Electromagnetic Waves
B. Energy and Light
• Dual wave-particle nature of light
– Wave
– Photon – packet of energy
B. Energy and Light
• Different wavelengths carry different
amounts of energy.
The Nature of Matter
• Matter and energy are not distinct!!!
– Max Planck
• Question: Is energy continuous? (Transfer of any
quantity of energy is possible)
• Experiment: studied the radiation bodies emitted
by solid bodies heated to incandescence.
• Result: matter could absorb or emit any quantity of
energy.
• Conclusion: energy can be gained or lost only in
whole-number multiples of the quantity h (energy
is quantized and can only occur in discrete units of
size h). Energy has particulate properties
Energy is Quantized
• E = h
– h = Plank’s constant (6.626 * 10 –34 J*s)
–  = frequency of electromagnetic radiation
absorbed or emitted.
• Each of these small packets of energy is called a
quantum.
• A system can transfer energy only in whole
quanta
• Therefore, energy seems to have particulate
properties.
Pickle Light
The Energy of a Photon
• Albert Einstein proposed that
electromagnetic radiation is itself quantized.
– Hypothesis: electromagnetic radiation can be
viewed as a stream of “particles” called photons
– Ephoton = h = hc

– h = Plank’s constant (6.626 * 10 –34 J*s)
–  = frequency of electromagnetic radiation
absorbed or emitted
–  is the wavelength of the radiation
C. Emission of Energy by Atoms
• Atoms can give off light.
– They first must receive energy and become excited.
– The energy is released in the form of a photon.
Photoelectric Effect
• Electrons are emitted from the surface of a metal when
light strikes it.
• Electromagnetic radiation is absorbed by matter
only in whole numbers of photons.
• In order for an electron to be ejected from a metal
surface, the electron must be struck by a single photon
possessing at least the minimum energy required to
knock the electron loose
• The minimum of energy corresponds to the
minimum of frequency.
Photoelectric Effect
– Photon’s frequency is below the minimum, then the
electron remains bound to the metal surface
– Different metals require different minimum
frequencies to exhibit the photoelectric effect.
– The KE of the emitted electrons increases linearly
with the frequency of the light with a frequency higher
than the threshold frequency.
The Photoelectric Effect
Photoelectric Effect
• Electromagnetic radiation is quantized (consists
of photons), and the threshold frequency
represents the minimum energy required to
remove the electron from the metal surface.
KEelectron = ½ m2 = h - h0
• The intensity of light is a measure of the number of
photons present in a given part of the beam
• A greater intensity means that more photons are
available to release electrons.
Planck & Einstein’s Results:
• Energy is quantized. It can occur only
in discrete units called quanta.
• Electromagnetic radiation and
electrons have dual wave-particle
nature.