Modern Physics Unit
Regents Physics
1 | P a g e
6.1.1 Photons, Photoelectric Effect, and Particle Nature of Light
Planck’s Constant
• Max Planck invented the concept of the _____________________ to explain the problem of Blackbody Radiation.
• Derived the constant ___________________________________ to describe the scale of energy increments allowed in atoms.
• Energy going into and out of atoms is _____________________. But why?
Photoelectric Effect
• Expectations from classical wave model of light.
- Higher intensity (brighter light) = greater amplitude o Should produce same # of faster electrons - Higher frequency (different colors) = more waves per second
o Should produce more electrons at same speed • Actual outcome…
- Brighter light gives more electrons per second
- Different colors give different electron speeds or stop the effect
• Albert Einstein uses the concept of the quantum to explain the Photoelectric Effect. • Invents the idea of the __________________________ which has an energy related
to Planck’s Constant and its frequency.
Einstein’s Model
For Einstein’s explanation to be correct, light is NOT a wave! It must be made up of particles. The particles each carry a certain amount of energy that is related to the light’s frequency.
So, we have phenomenon that show that light MUST be a wave…
but the _______________________________________________ shows that light MUST be made up of particles…
SO WHICH IS IT?!?
Photon Properties
- Massless
- Carry energy and momentum - Travel at the speed of light
- Have particle-like collisions - ________________________________
Equation
outgoing electrons light
“waves”
metal plate
metal plate beam
of light a brighter beam
means MORE photons
Each photon has a chance to liberate an electron but the photon must have enough
energy (the right frequency)
e- v
v = 0
e-
Example #1
• What is the energy of a photon with a wavelength of 4.5 x 10-7 meters? What type of photon is it?
Example #2
• If a photon has 7.0 x 10-3 joules of energy, what frequency does it have? What type of photon is it?
Wave/Particle Duality
• In 1924 Louie de Broglie proposed that because light has properties of particles that it might be possible for matter to exhibit the properties of waves.
• This was proven to be true by ________________________________ experiments demonstrated by Davisson and Germer in 1927.
• While particles do seem to have a particle nature, this is only evident for
__________________________________________________________.
Mass/Energy Duality
• In 1905, Einstein publishes his paper on Special Relativity. • This paper proposes
__________________________________________________________________ __________________________________________________________________ _____________________________________________.
PRACTICE
1. How much energy would be released if a 7.0 kilogram mass was completely converted into energy?
2. How much energy is contained in 2.0 universal mass units?
Modern Physics Unit
Regents Physics
3 | P a g e - What type of photon has an energy of 9.0 x 10-19 joules?
[Ultraviolet]
6.1.1d – Demonstrate understanding of wave/particle duality.
- Which of the following could be used to demonstrate the wave properties of matter?
o asteriod o electron o bicycle o proton o apple
6.1.1e – Demonstrate understanding of mass/energy duality. Use equation to determine relationship between energy and mass. Be able to convert between universal mass units and mega-electron-volts.
- How much energy is contained in 3.0 kilograms of matter?
[2.7 x 1017 J]
- How much mass is needed to produce 2.0 mega-joules of energy?
[2.2 x 10-11 kg]
-
How much energy is contained in 5.0 univseral mass units of matter?[4655 MeV]
Review Questions 6.1.1a – Demonstrate underrstanding of energy quantization.
- Explain why an atom of a given element can produce only specific photons of light when heated.
6.1.1b – Demonstrate understanding of wave/particle duality of light. - Light exhibits properties of
(1) waves only (2) particles only (3) both waves and particles
- Give one example of a phenomenon or expriment that demonstrates: (1) The wave nature of light : ______________________________ (2) The particle nature of light: _____________________________
6.1.1c – Demonstrate understading of photon properties. Use equation to determine photon energy, frequency, and/or wavelength. Use EM Spectrum Chart to determine photon type.
- What is the energy of a photon with a frequency of 2.5 x 1013 hertz?
[1.7 x 10-20 J]
- What is the wavelength of a photon with an energy of 3.0 x 10-18 joules?
Ionization
Example #1
• A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
o What minimum energy did this photon have?
o What is the frequency of the photon that could provide this energy?
Example #2
• What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?
Level Jumps
• An electron will jump to a higher level if the __________________ photon has EXACTLY the right energy.
• When an electron drops to a lower level a photon is __________________.
Example #3
• What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level?
Equation
________________ ________________
Energy needed to liberate electron
from that level. __________________
______________ Lowest possible energy state in an
Modern Physics Unit
Regents Physics
5 | P a g e
Example #4
• An electron drops from the n = 4 level to the n = 3 level of hydrogen o What is the energy of the photon emitted?
o What is the frequency of this photon?
Example #5
• When electrons drop from one energy level to another they can follow any path to the lower state. Each downward step produces a photon with a different energy.
o How many different photons could be produced in a transition from the n = 4 level of hydrogen to the n = 1 level?
o How many different photons could be produced in a transition from the d-level to the b-level of a mercury atom?
Spectrums
• An ___________________________________ is a pattern of bright lines on a dark background.
o Analyze glow of a heated sample.
• An ___________________________________ is a pattern of dark bands on a continuous spectrum.
o Pass white light through a cold sample.
• The existence of spectrums demonstrates that:
o Energy in atoms is _____________________ - comes in discrete jumps. o Atoms can produce only specific sets of ___________________.
Hot Gas Emitted
Photons Prism
Bright Line Spectrum
White Light All frequencies
Cold Gas
Transmitted Photons – most come
through
Prism
Gaps in Spectrum of White Light
- An electron in the d-level of a mercury atom drops to the ground state. How many different photons could be produced during this transion?
[6]
- Explain why a 3.0 electron-volt photon will have no effect on an electron in the n=2 level of a hydrogen atom.
6.1.2c – Understand the importance and meaning of the emission and absoprtion spectrum. Identify the components of a sample by its spectrum.
- Use the spectrums below to determine which of the four samples contain “Element X”.
[A, D]
A B C D Spectrum for Element X
6.1.2a – Determine ionization energies and kinetic energies for liberated electrons. - What energy is needed to liberate an electron from the c-level of a mercury
atom?
- A hydrogen atom with an electron in the n = 3 level is hit by a photon with an energy of 2.51 electron-volts. What kinetic energy will the electron have as it leaves the atom?
[1.0 eV]
6.1.2b – Use equation to determine the outcome of a photon absorption, emission, or an energy level transition. Convert from joules to electron-volts; determine photon energy and/or frequency and type using the EM Spctrum Chart.
- A photon causes n electron to jump from the b-level to the e-level of a mercury atom. What energy did this photon need to have? What was its frequency? What type of photon was it?
[-2.03 eV / 3.2 x 10-19 J
4.8 x 1014 Hz / visible]
-
A 10.2 eV photon is emitted by an electron in a hydrogen atom as it returns to the ground state. What energy level did the electron drop from?[n = 2]
-
What photon energy is needed to cause an electron to leave the h-level of a mercury atom with a kinetic energy of 4.0 electron volts?Modern Physics Unit
Regents Physics
7 | P a g e
6.1.3 Standard Model
Definition
A theory that describes three of the four fundamental forces of nature and the various particles that make up matter in the Universe. This theory is consistent with Relativity and Quantum
Mechanics.
Classes of Matter
Made up of ____________________ and their ________________________ with ________________________ mass and ______________________ charge.
Example #1
• What charges are allowed for mesons?
Example #2
• Give an example of a baryon with a +1e charge.
Example #3
• What is the charge on an anti-tau particle?
Example #4
• A charged kaon (K+) is composed of an up quark and an anti-strange quark. What is the charge on this type of kaon?
Fundamental Forces
Force Range Strength Carrier What it does
Strong Nuclear 10-15 m 1 gluons Holds nuclei together
Electromagnetism Infinite 1/137 photons Holds atoms and
molecules together
Weak Nuclear 10-18 m 10-6 W & Z
bosons beta decay
Gravity Infinite 10-39 graviton? Holds objects with mass
together
Beta Decay
A neutron will spontaneously decay into a proton, electron, and anti-electron neutrino.
Matter
Hadrons Leptons
Do not experience the strong force
tau (τ-) -1e
muon (μ-) -1e
electron (e-) -1e
τ neutrino (ντ0)
μ neutrino (νμ0)
e neutrino (νe0)
Anti-Leptons
anti-tau (τ +)
anti-muon (μ +)
anti-electron ( +)
anti-τ neutrino (ν τ0)
anti-μ neutrino (ν μ0)
anti-e neutrino (ν e0)
Baryons
any 3 quarks
Anti-Baryon
any 3 anti-quarks
Mesons
any quark plus any
anti-quark
Quarks
+2/3e u t c
-1/3e d b s
Anti-Quarks
-2/3e
6.1.3b – Describe the fundamental forces of the Standard Model. Explain the operation of the strong force and beta decay.
- What is the function of the strong force?
- What force is responsible for beta decay?
- Which fundamental force is still unexplained by the Standard Model?
- Which of the particles would not be effected by the electromagnetic force? (1) electron
(2) anti-muon (3) tau-neutrino (4) ucb (5) udd
[3,5]
- Which of the particles would not be effected by the strong force? (1) proton
(2) meson
(3) electron-neutrino (4) muon
[3,4]
Review Questions
6.1.3a – Classify and determine the charge of various particles.Explain how matter and anti-matter are related.
- Classify each of the following as either a: lepton, lepton, baryon, anti-baryon, meson or ‘not enough information’.
(1) A particle made of 3 quarks. (2) A particle with no charge. (3) An electron.
(4) A neutron.
(5) A particle composed of an up quark and an anti—down quark. (6) A particle composed of three anti-up quarks.
(7) A muon-neutrino.
(8) A particle with a charge of +2. (9) An anti-electron.
[B,X,L,B,M,AB,L,B,AL]
- What is the charge on a particle containing two down quarks and one up quark?
[0e]
- What is the charge on a particle containing a down quark and an anti-up quark?
[-1e]
- A hydrogen atom consists of a proton and an electron. An anti-hydrogen atom consists of an anti-proton and an anti-electron(positron). Explain the
differences and similarities between hydrogen and anti-hydrogen in terms of mass, charge, and emission spectrum.
[same in every way]
- A proton is constructed using the quark configuration uud. Confirm that this produces a charge of +1. An anti-proton is built using the quark configuration
d u
