# 7- Modern Physics

## Slideshow: Nuclear & Modern Physics

Textbook: Lightweight coverage of chapters 25, 26, 27, 28 & 29

Must watch: Quantum Physics video: https://youtu.be/Usu9xZfabPM

## Objectives

• Structure of particles
• Fundamental Particles have no internal structure
• Electrons, neutrinos, photons and quarks are fundamental (not made of other things)
• Neutrons and Protons are both made of 3 quarks.
• Quarks are fundamental and have a partial charge, but combine to be either neutral or a complete fundamental charge
• supporting ideas not directly tested
• Know how protons and neutrons and electron numbers can be found from atomic number and mass number.
• know about how half half life works.
• Atomic structure
• ions have different properties than neutral atoms
• Energy level structure of atoms
• discrete energy states of atoms (bohr model) lead to spectra
• emission spectrum can be used to determine the elements in a source of light.
• Nucleon interactions are dominated by the nuclear strong force, which only works at extremely small scales.
• Gravitational mass and inertial mass
• differentiate inertial mass and gravitational mass, but explain that we have found the values to be the same.
• E = mc2 indicates that we should have a mass-energy conservation law as opposed to just our mass conservation law. (from special relativity)
• mass and energy are two forms of the same entity/property
• mass and energy can be converted from one form to the other.
• significant energy can be produced by nuclear processes.
• Wave particle duality
• wavelike particles, like electrons, can exhibit diffraction
• we only see the wave properties of matter at small scales
• Î»=h/f to find the de broglie wavelength of a particle.
• light (classically a wave) shows particle behavior.
• light has quantized energy and has momentum only explained by photon (particle) behavior, while still exhibiting wave behaviors
• energy transfer occurs when photons are absorbed or emitted by atoms or nuclei.
• Relativistic explanations work where classical physics breaks down.
• Classical physics does not work to predict behaviors at very high rates of speed (like 75% c)
• measurements of length and time depend on speed (observers disagree on length and time measurements based on FOR)

## Common Misconceptions

### Models of the Atom

• There is only one correct model of the atom.
• Electrons in an atom orbit nuclei like planets orbit the sun.
• Electron clouds are pictures of orbits.
• Electrons can be in any orbit they wish.
• Hydrogen is a typical atom.
• The wave function describes the trajectory of a electron.
• Electrons are physically larger than protons.
• Electrons and protons are the only fundamental particles.
• Physicists currently have the "right" model of the atom.
• Atoms can disappear (decay).

### Wave Particle Duality

• Light is one or the other--a particle or a wave--only.
• Light can be a particle at one point in time and a wave at another point in time.
• Particles can't have wave properties.
• Waves can't have particle properties.
• The position of a particle always can be exactly known.
• A photon is a particle with a wave inside.
• Photons of higher frequency are bigger than photons of lower frequency.
• All photons have the same energy.
• Intensity means that the amplitude of a photon is bigger.
• The Uncertainty Principle results from the limits of measuring devices.
• Laser beams are always visible by themselves.
• Sometimes you feel like a wave, sometimes you don't.

### Michelson Morely Experiment

• A null result means experiment was a failure.
• The aether exists because something must transmit light.
• Relativistic effects (length contraction) is the reason why no difference in the speed of light
• was observed.

### Special Relativity

• Velocities for light are additive like for particles.
• Postulates cannot be used to develop a theory.
• Length, mass, and time changes are just apparent.
• Time is absolute.
• Length and time only change for one observer.
• Time dilation refers to 2 clocks in 2 different frames.
• Time dilation and length contractions have not been proven in experiments.
• There exits a preferred frame of reference in the universe.
• A mass moving at the speed of light becomes energy.
• Mass is absolute, that is, it has the same value in all reference frames.

### Curved Space and Black Holes

• Space is not something.
• Black holes are big.
• Light always travels in straight lines.
• Black holes exert a greater gravitational force on distant objects than the star from which it
• was formed.
• Observations made in a gravitational field are different that those made in a system undergoing
• constant acceleration.
• Things in space make sounds.
• If the Sun were to become a black hole, the Earth would get sucked into it.

### Wave Nature of Light

• Velocities for light are additive like for particles.
• Postulates cannot be used to develop a theory.
• Length, mass, and time changes are just apparent.
• Time is absolute.
• Length and time only change for one observer.
• Time dilation refers to 2 clocks in 2 different frames.
• Time dilation and length contractions have not been proven in experiments.
• There exits a preferred frame of reference in the universe.
• A mass moving at the speed of light becomes energy.
• Mass is absolute, that is, it has the same value in all reference frames.