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Modern Physics

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Mr. Emhardt

on 5 May 2016

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Transcript of Modern Physics

Modern Physics
Dual Nature of Light

• Light exhibits the characteristics of both waves and particles.
• When light interacts with itself it behaves like a wave.
• Interference, polarization, and diffraction are most easily explained using wave theory.
Dual Nature of Light
Classification of Matter
Modern model of the atom
Conservation of Mass and Energy
Mr. Emhardt
Regents Physics

• Max Planck - When an atom emits light, the energy of the atom changes by quantized amounts.
• Albert Einstein - Carried this idea out further and said that light itself is quantized.
• When light interacts with matter, it behaves like a particle.
• Tiny particles of light are called photons.

• Photons act like any particle and posses KE and momentum when they are in motion.
Particle Theory
The energy contained in a photon of light is represented by: E=hf
is the frequency of light (Hz)
is Planck’s constant

1. What is the wavelength of a quantum of light having a frequency of 6.0 x 10^14 hertz?

2. What is the wavelength of a photon with a frequency of 5.00 x 10^14 hertz?

3. A photon of light traveling through space with a wavelength of 6.0 x 10^-7 meter has an energy of

Photoelectric Effect

• The emission of electrons from a metal as a result of radiation is called the photoelectric effect.
• This emission of electrons results from the absorption of energy from the photons
• The emitted electrons are called
• The absorption of a photon by an atom in a metal surface is an all or nothing process.
Quantum Theory

• E = hf E = hc / λ
• Energy - Directly proportional to f - Inversely proportional to λ
f = Frequency, Hertz (Hz)
λ = Wavelength, Meters (m)

What are the Fundamental Particles?
They are called quarks and leptons
Three quarks make up protons and neutrons
An electron is an example of a lepton

Regents Questions
1. A lithium atom consists of 3 protons, 4 neutrons, and 3 electrons. This atom contains a total of

a)21 quarks and 3 leptons c)9 quarks and 7 leptons
b)12 quarks and 6 leptons d)14 quarks and 3 leptons

2. Which combination of three quarks will produce a...
(a) neutron
(b) Proton
What is the general charge of a Proton?

What is the general charge of a neutron?
Protons made up of 2 positive and 1 negative quark

Neutrons made up of 2 negative and 1 positive quark
Bohr Model
e- can gain or lose energy only in fixed amounts. Energy is quantized.

e- can occupy only specific orbits of fixed radius.

Each orbit corresponds to a specific amount of energy.

The ground state is the most stable state and the lowest possible energy level.

Atomic Energy Levels
e- can jump from one orbit to a higher orbit by absorbing a quanta of energy.

e- releases a quanta of energy by going from a higher orbit to a lower orbit. This release of energy is in the form of a photon.

This photon has a a specific frequency associated with the energy loss.

Regents Practice
An electron drops from the n=3 energy level to the n=2 energy level within a hydrogen atom.
Determine the energy of the photon emitted.
Calculate the frequency of the photon emitted.
Calculate the wavelength of the photon emitted.


11. What is the minimum energy required to ionize a hydrogen atom in the n = 3 state?
a) 12.09 eV
b) 5.52 eV
c) 13.60 eV
d) 1.51 eV

12. A hydrogen atom could have an electron energy-level transition from n = 2 to n = 3 by absorbing a photon having an energy of

a) 10.20 eV
b) 4.91 eV
c) 1.51 eV
d) 1.89 eV

13. An excited hydrogen atom returns to its ground state. A possible energy change for the atom is a

a) gain of 3.40 eV
b) loss of 3.40 eV
c) loss of 10.20 eV
d) gain of 10.20 eV

6. The electron in a hydrogen atom drops from energy level n = 2 to energy level n = 1 by emitting a photon having an energy of approximately
a) 7.4 x 10^-18 J
b) 2.2 x 10^-18 J
c) 5.4 x 10^-19 J
d) 1.6 x 10^-18 J

Converting electronvolts (eV) to Joules (J)

9. Which type of photon is emitted when an electron in a hydrogen atom drops from the n = 2 to the n = 1 energy level?
a) radio wave
b) ultraviolet
c) infrared
d) visible light

Do Now
1)What is the energy of a quantum of light having a frequency of 6.0 x 10^14 hertz?

2)What is the frequency of a photon whose energy is 4.64 x 10^-20J?
Conservation of matter
Matter and energy cannot be created or destroyed...

But they can be converted into another form
E= energy (Joules (J))

m = mass (kilograms (kg))

c = speed of light in a vacuum (3.00x10^8 m/s)
Ex) ***Energy that can be obtained from converting 2.0 Kg to energy?
E = ?

m = 2 kg

c = 3.00 x 10^8 m/s
1. The energy equivalent of 5.0 x 10^-3 kilogram is
a)3.0 x 10^19 J b)1.5 x 10^6 J c)8.0 x 10^5 J d)4.5 x 10^14 J

2. The energy produced by the complete conversion of 2.0 x 10^-5 kilogram of mass into energy is
a)1.8 TJ b)6.0 GJ c)6.0 kJ d)1.8 MJ

3. What is the energy equivalent of a mass of 0.026 kilogram?
a)2.34 x 10^17 J b)2.34 x 10^15 J c)2.3 x 10^17 J d)2.3 x 10^15 J

4. How much energy would be generated if a 1.0 x 10^-3 kg mass were completely converted to energy?
a)9.3 x 10^2 MeV b)9.3 x 10^-1 MeV c)9.0 x 10^13 J d)9.0 x 10^16 J

Universal Mass Units
a fundamental principle of classical physics that matter cannot be created or destroyed in an isolated system
Conservation of energy
A principle stating that the total energy of an isolated system remains constant regardless of changes within the system.
Forces Inside the Nucleus
Review / Reference Table Practice
List these electromagnetic waves from highest to lowest energy

Green Light
FM Radio
Orange Light
Gamma Rays
AM Radio
Gamma Rays (~10^19 - 10^21Hz)
Ultraviolet (~10^15 - 10^18 Hz)
Green (~6x10^14Hz)
Orange (~5x10^14Hz)
Microwaves (~10^9 - 10^12Hz)
FM Radio (~10^8Hz)
AM Radio (~10^6Hz)
Higher Frequencies means Higher Energies
Higher Frequencies mean Shorter Wavelengths
Shorter Wavelengths also means Higher Energies
Frequency and Wavelength
Frequency has an inverse relationship with wavelength.
Product of frequency and wavelength is the wave's velocity
Since all electromagnetic waves travel at the speed of light,
c=f λ
f = frequency (Hz)
λ=wavelength (m)
c=speed of light in vacuum (3 X 10^8m/s)
Frequency has a/an _______ relationship with energy
(meaning as frequency goes ____ energy goes _______)

Wavelength has a/an ________ relationship with energy
(meaning as wavelength goes _____ energy goes ______)
In order to convert electronvolts into joules I would _______ by 1.6 x 10^-19
In order to convert joules into electronvolts I would ___________ by 1.6 x 10^-19
How many joules of energy is created when a proton is completely converted into energy?

1 proton = 1 universal mass unit
1 universal mass unit = 931 Mev
amount of energy that is obtained from converting a single proton into energy

How much energy can be generated when 2 universal mass units are completely converted into energy?

Regents Practice
Strong Force - Binding Force holding the nucleons together inside the nucleus
Very Strong over Very Short Distances
Weak Force - causes decay in atoms
only works over VERY VERY short distance
Four Fundamental Interactions (forces) of the Universe
Gravitational - Causes matter to be attracted because of their masses. Weakest force, but longest range

Electromagnetic - Matter is attracted or repelled because of its electrical charge. Very strong force, but short range

Strong - Holds the nucleus of an atom together. Strongest force, but very very short range (the size of a medium nucleus)

Weak - Don't worry about it.
If a deuterium nucleus has a mass of 1.53 x 10 universal mass units less than its components, this mass represents an energy of
Direct Relationship -
two variables that one changing causes the other to change in the same way
(up, up or down, down)
Dual Nature of Light
- light has both wave-like and particle-like properties
- To give off or remove (emit)
Fundamental -
The most basic / smallest
Ground State
- most stable, lowest energy level of an atom
Indirect Relationship -
two variables that one changing causes no change in the other
- an atom that has either gained or lost an electron resulting in a negative or positive charge respectively
Inverse Relationship
- two variables that one changing causes the other to change in the opposite way
(up, down or down, up)
Photoelectric Effect
- When light strikes a metal surface with the correct frequency electrons are emitted from the metal
- a particle of light (Energy)
- Grouped in a specific quantity or value (stairs, not hills)
- same qualities as a normal quark only with an opposite charge
(-2/3 or +1/3)
written with a bar above it ( u, d )
- Particle that is made up of three quarks (proton or neutron)
- fundamental particle that makes up protons and neutrons. Have a charge of +2/3e or -1/3e
- electron
- Composed of 1 quark and 1 antiquark
Strong Force
- Force that holds the nucleus together

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