Physics - Introductory Berkeley course

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All notes by John Eagles

Introduction

Today I started watching this introductory course in physics. It's a UC Berkeley course given by Richard Muller. He explains physics without using many equations. In this particular lecture he comments quite a bit on 9/11 related physics and dwells on terrorist shoe bombs. He advises the government in such matters, so his views seem a bit politically colored. But he really knows how to present laws of physics in a very understandable and close-to-life manner. I've learned quite some new things from watching this lecture.

Solar technology, coal reserves

Summary of topics lectured about:

Calories of food
Peripheral vision of the eyes detect especially motion
Solar technology
Tilt of the earth & the seasons
Global warming in relation to the forming of clouds. When the climate heats up, more clouds may form and may counter the greenhouse effect.
Canada is 2nd in the world after Saudi Arabia for its oil reserves, but Canada has it stored in oil sand and it's more expensive
Natural gas & shale gas in comparison to oil
Coal reserves: The USA has most reserves, then comes Russia and then China, Australia and India. These reserves are big in terms of energy compared to the world's oil reserves.
Coal and methane can turned into gasoline, but it's still risky in case the oil prices are lowered.
In politics, there's conflict between the issues of global warming and energy security.
Coal is the cheapest form of energy.
IPCC errors
Sequestering CO2 and making clean use of coal
CCS = Carbon Capture & Storage

Temperature scales

Topics in this video:

Size of atoms
Density of atoms
What makes atoms move, what gives them the kinetic energy?
Temperature = how much energy do things have
Thermometers
Scales of Celcius, Fahrenheit
Liquid nitrogen experiments
There are ca 1000 x more molecules in a fluid than in a gas of the same substance per volume
Temperature of absolute zero on the Kelvin scale means there is no energy
In the Kelvin scale the amount of energy is proportional to the temperature
A fire extinguisher has liquid CO2
Your subjective temperature measurement
Hot air rises because it's less dense
Conduction, convection, radiation

Lecturer is Bob Jacobsen

Thermodynamics intro

The ideal gas law (relationship between volume & temperature)
Movements of small and bigger molecules and atoms
Energy efficiency of engines
Refrigerators
Air conditioners
Entropy = a measure of disorder

Satellites, gravity

This lecture is about:

Friction
Movements of satellites
Why frisbees and airplane wings lift
Satellites move with 5 miles per second. They are falling but because the earth is curved, they fall with the earth curve
Rockets escape velocity
Gravity force between two people near to each other is ca mass of a mosquito
What does it mean to be weightless
How do spy satellites work. They have to be close to the ground. It takes them 1 1/2 hour to orbit the earth one time.
Unmanned drones
Weather and tv satellites orbit the equator at 22000 miles high and need 24 hours for one cycle: Geostationary satellites
24 GPS satellites go around in 12 hours.

Newton's laws, inertia, circular motion

Topics explained in this lecture, illustrated with several experiments:

Newton's laws
Inertia
Circular motion

Radiation, radioactivity

Ionizing radiation knocks electrons off atoms.
We're exposed to some amount of ionizing radiation all the time.
Tritium is used in some watches.
Damaging of DNA is what causes cancer.
Sieverts - Grays - rems.
2500 rems (25 Sieverts) on average causes 1 fatal cancer. It's a probability.
Radiation illness - requires much less than a dose causing cancer.
About percentages of increase of cancer because of radioactivity.
Alpha rays don't penetrate deeply, are stopped by the skin.
X-rays.

Global warming, radioactive rays, radiocarbon dating

Categories of believers and non-believers in global warming.
Errors in IPCC reports
He quotes research stating that organic food is unhealthy?!?
Chemotherapy & radiation therapy against cancer, how does it work?
The energy release of exploding a nucleus is typically 1 million times more than energy released in chemical reactions.
In the early universe almost all atoms probably were explosive or radioactive.
Radiocarbon dating with C14, having a half-life time of 6,000 years. C14 is in the atmosphere because of cosmic radiation affecting C atoms. Living organisms take in a percentage of these C14 atoms. The amount of C14 in the atmosphere is constant.
Potassium-Argon dating: A dating method using rocks.
Beta rays are fast electrons.
Alpha rays consist of small nuclei of 2 protons and 2 neutrons that form He atoms when the rays are stopped.
Gamma rays are penetrating, not ionizing colliding particles. They pass through things. They knock off electrons and are very energetic.
X rays are the same as gamma rays but more energetic. X-ray photos create shadows.

Nuclear reactors, uranium, chain reactions

This lecture is about:

How to get useful energy from radioactive elements.
Chain reactions and nuclear fission.
U235 is more radioactive than U238, but there's much less of U235 on earth (U = uranium).
Enrichment of uranium is removing what you don't want, for example by using centrifuges.
Depleted uranium.
Natural and oldest man-made nuclear reactors.
The nature of chain reactions.

Nuclear waste, fusion reactors

Where to store nuclear waste?
Safety measures for nuclear plants.
Spent fuel rods and spent fuel storage installations.
Nuclear waste transport.
Waste from uranium mines.
Fusion reactors are still not commercially operated.

Graphene, electricity basics

Four different carbon bonds.
Graphite and graphene. Graphene is a newly produced one-layer sheet of graphite.
Sparks from static electricity.
Voltage, currents, resistance.
Fuses and circuit breakers.
Electrocution.
Fibrillation of the heart.
AC and DC currents.

Magnetism

What is magnetism?
Rare-earth magnets have transformed society.
Rare-earth minerals.
The earth is a magnet.
Magnetism comes about when there is a moving charge.
Magnetic recording, hard disks, credit cards.
Electric generators = moving wires pass a magnet.
Transformers.
Voltage is energy per electron.
Magnetic levitation.

Scientific implications of magnetism - Electrical power

Power = voltage x current.
A moving magnetic field makes voltage and provided there is a conductor, a current.
Alternating currents and direct currents (AC and DC).
Edison's first promoting of his electric bulbs.
High-voltage wires.
Smart grids.

Waves

Seismographs measure the shaking of the ground.
Atoms are basically a kind of waves, quantum waves.
A particle is a wave.
When you shake the vacuum it becomes a wave.
A wave is moving energy.
The old concept of 'aether' is now renamed 'vacuum.'
Different types of waves.
Earthquakes & tsunamis.

There's a funny interruption of the lecture because of student demonstrations.

More about waves

Waves have three characteristics:
- Amplitude (height or size)
- Energy (intensity or power)
- Speed (small and big waves travel at the same speed)
Strings of music instruments.
Piano tuning.
Interference of sound waves.
Sound waves.
Interference of FM radio waves.
Mirages.

Mechanical waves

Mechanical waves transport energy through a medium by elastic deformations.
Characteristics of mechanical waves:
- The medium itself has no position, oscillates around a fixed position.
- Energy is required to create a wave. The wave transports the energy.
- Waves can transmit information.
- Waves travel with a fixed speed for a given medium (wave speed).
A wave pulse is a single propagating disturbance.
Periodic waves repeat regularly.
Frequency = cycles per second (Hertz).
Mechanical waves require a medium (inertia of the medium), and a form of restoring force (pushing the medium back to a starting position).
Superposition of waves: Bouncing waves don't affect each other in terms of the speed with which they travel and the energy they carry.
Standing waves form when two identical waves travel in opposite directions.
Standing waves on guitar strings.
1st, 2nd, 3rd harmonics on strings.

Sound, open and closed pipes

Sound is longitudinal or compression waves. They can be through any medium with molecules (gas, liquids, solids), not a vacuum.
Sound is pressure waves, or alternating regions of high and low pressure.
Speed of sound in air is ca. 340 m/s.
Air inside a pipe, shock waves inside a pipe.
The closed end in a pipe always feels the maximum pressure of the wave.
At the open end of a pipe the molecules are free to move. It's a pressure node, the pressure doesn't change.
Wind instruments are resonant pipes, open or closed.
A flute is an open pipe.
A clarinet is a closed pipe.
Open pipes have all harmonics.
Closed pipes have only odd harmonics.
Beats.
Doppler effect.

Electricity

Electricity is transfer of power or information by electrical forces.
Electrostatic force: A fundamental force of nature (like gravity).
Applications:
- transfer of power
- storing energy in batteries
- run appliances
- light, heat
- transportation
- computers, telecommunication, entertainment
This force comes from electrical charges.
Electrons have about 1/2000th of the mass of neutrons and protons.
Electric charges come in two types: Positive and negative.
Protons and electrons have exactly equal and opposite charges.
There is a fundamental unit of charge.
Electrons move much easier than protons.
Conservation of charge:
- The universe has no net charge (is what is believed)
- We cannot create a positive or negative net charge
The electrostatic force is both attractive and repulsive.
The gravitational force is only attractive.
Electrostatic force : gravity = 4 x 10 to the 42 : 1, so the electric force is much stronger.
Conductors and insulators
Electrostatic potential energy.

Electrical current & circuits

Voltage = Potential energy / charge.
Batteries = Chemical charge pump. Chemicals store energy which is converted to voltage.
Electrical outlets: The ground of an outlet is literally connected to Earth. It is to keep you and the socket at the same voltage.
Solar cells: Directly convert sunlight into electrostatic charge.
For a voltage to provide power, a charge must flow. This is an electrical current.
Negative charges (electrons) flow from negative to positive. The currents flows in the other direction.
Electrical circuits:
- Current is usually confined to flow in wires to appliances.
- No current can flow in an open circuit.
Electrical power:
- Voltage = Potential energy / charge
- Current = Charge transfer / time
- Power = Voltage x current
Resistance limits the amount of current flow through a circuit for a given voltage.
Voltage drop
Ohm's law: Voltage drop = current x resistance.
Current = Voltage drop / resistance.
Power lost = current² x resistance

Magnetism

Is closely tied to electricity.
Simple magnets have some analogies to electrical charges.
A magnetic 'charge' is called a magnetic pole.
Two types of poles: North and South.
These poles always appear in opposite pairs. We call this a dipole.
Magnetic dipoles are similar to electric dipoles.
But there is one major difference: Electric positive and negative charges can exist independently but magnetic monopoles don't exist.
Electromagnets:
- Oersted in 1820 discovered that electric currents produce magnetic fields.
- On the microscopic level electrons orbit in an atom causing electrical currents.
- For most atoms these currents cancel because electrons orbit in different directions.
- Iron is an exception. Multiple electrons in iron atoms are orbiting in the same direction.
- Each atom is a little atomic magnet.
- Magnetism is a product of electrical forces.
- Magnetic materials, iron and steel, consist of many microscopic atomic magnets. These usually are not aligned.
- Faraday showed that a changing magnetic field produces electrical currents.
- And electrical currents produce magnetic fields.

Light

How do we see an object? Light from the object must enter our eyes as a source of light, as reflected light or as an optical image using lenses or mirrors.
Light is both a wave and a particle, but light doesn't need a medium to travel.
Light interacting with a surface, for ex. water: Light can get absorbed, bounce off or be reflected, pass through or be refracted.
Two types of reflection:

Specular reflection is off a smooth surface, like mirrors. Light is scattered in one direction.
Diffuse reflection is off a rough surface (most surface). Light is scattered in all directions.

Selective absorption: Some colors are preferentially absorbed, other colors are reflected.
Without atmosphere we would see the sky as black. Air preferentially scatters blue light over red light.
Refraction: Light travels slower in any material. The light will turn when it enters the new medium.
Violet light turns more than red light.
Rainbows.
Total internal reflection - light can stay trapped in a denser medium. Application of this principle in fiber optics.
Lasers are coherent light. All laser light has one color and the light travels all in one direction. It is very intense.

Nuclear structure

Elements are defined by the # electrons which equals the # protons. This defines the chemistry of the element.
Isotopes are determined by the # neutrons in the nucleus of a given element.
For example 235U has 92 protons + 143 neutrons = 235 nucleons.
Isotopes are chemically identical but very different in nuclear reactions.
Most isotopes are stable, do never change; some are unstable and undergo radioactive decay.
Neutrons in nuclei are generally stable but free neutrons decay with a half-life of ca. 10 minutes.
Neutrons decay into a proton + electron.
The nuclear force is also called Strong Force. This is an attractive force between all nucleons. It is confined to a very short distance.
Nuclear stability means there is a balance between electrostatic repulsion of protons and the strong force attraction between all the nucleons.
Not all combinations of neutrons and protons are stable.
More neutrons are needed when there are more protons.
If there are too many neutrons the neutrons will decay.
Above 83 protons all nuclei are unstable.
Radioactivity is the result of unstable nuclei.
Half-life ranges from 10^-6 seconds to 10⁹ years.
Three types of radioactivity are alpha rays, beta rays and gamma rays.
Alpha decay is emission of a He nucleus. He has 2 protons and 2 neutrons and has a very solid structure. Alpha decay tends to increase the neutron to proton ratio. It is easily stopped by the skin or by air, but are very damaging when swallowed or breathed.
Beta decay is emission of electrons from neutron decay. It decreases the neutron / proton ratio and makes the nucleus more stable. Beta decay is easy to stop.
Gamma decay is emission of gamma rays. These are high-energy particles of light. It releases excess energy in the nucleus, but doesn't change the nucleus otherwise. Gamma rays are harder to shield, are very penetrating. They are less damaging per decay. They are often used as tracers for medical imaging.
Radioactivity of the natural environment is ca 1/200th of what is fatal.

See also this video^[1] that gives much of the same information in a short overview.

Nuclear fission

Nuclear fission is splitting heavy nuclei apart to release energy.
For example, 235 U is a natural occurring isotope. In natural uranium is 0.7 % 235 U and 99.3 % 238 U.
235 U has 92 protons and 143 neutrons in the nucleus. Breaking the nucleus produces ca. 1 million times the energy of chemical reactions.
How to induce fission? Send in a neutron.
235 U splits apart by slow neutrons. 235 U is unique in this regard. It breaks apart in two smaller nuclei, 2 or 3 free neutrons + energy.
1 gram of 235 U equals the energy of 2.7 tons of coal.
A chain reaction takes place because a split 235 U atom releases 2-3 more neutrons.
Uncontrolled reaction gives an explosion. Controlled reaction is done in a reactor.
Uncontrolled reactions are hard to produce because:

Natural uranium contains 99.3 % of 238 U and this will absorb most neutrons.
Released neutrons travel fast and fast neutrons do not cause new fission. To slow the neutron a moderator is needed.

Fission rates

Critical - One additional fission per induced fission. This is the operational state of reactors.
Supercritical - Less than one neutron goes on to fission. This is a growing or explosive reaction.
Subcritical - Less than one neutron produces fission. This is a dying reaction.

Nuclear reactors currently produce ca 14 % of the world's electrical energy (2011).
Advantages of nuclear reactors: They don't cause carbon emission. There is between 100 to 1000 years of supply. They provide energy security.
Disadvantages: Reactors are expensive to build. Safety issues. They produce 231 Pu (plutonium), which is potential bomb material.

4 main components are needed in the core of a nuclear reactor. This is for the example of a Light Water Reactor.

Fuel, which produces fast neutrons. Normally this is 235 U mixed with 238 U enriched so there is ca. 3 % of 235 U.
A moderator which slows the neutrons. For a Light Water Reactor this is normal water.
Control rods to stop neutrons. Control rods control the reaction by inserting or removing the rods from the core. They usually are made of Boron or Cadmium.
A coolant that carries the energy out to produce electricity, and to keep the core from overheating.

Accidents at Three Miles Island, Fukushima, Chernobyl.
For weapons highly enriched uranium is needed with 20 % of 235 U.
Plutonium 239 is produced in all nuclear reactors. It is fissionable. Some reactors use plutonium as fuel.
Plutonium is very easy to separate chemically from uranium and can be used for weapons.

The Big Bang

Space is an actual physical property that can change.
Matter tells space how to curve, and space tells matter how to move.
The evolution of space and time are governed by the contents of the universe: Matter.
Te cosmological principle states that on a large scale the universe is basically the same everywhere, there are no unique vantage points.
Space is expanding but objects are not expanding.
In the very early universe only protons and neurons existed.
The explosion of the universe is accelerating.

Review accelerating universe and more

This lecture is mostly review.

Evidence for dark matter.
Experiments to measure dark matter.
Why is the night sky dark?
The accelerated expansion of the universe.
Dark energy.
In our time the force of gravity in the universe is equal to that of dark energy, which works in opposite direction.

Our solar system and possible life beyond it

Scale of the solar system.
The solar system is basically empty.
Kuiper Belt objects.
Beyond the solar system.
Life in the universe.
Pulsar stars.
SETI.
Some special telescopes.
Humanity's message into space.
Different kinds of galaxies.

References

↑ Radiation and Radioactive Decay

[1] Radiation and Radioactive Decay

[1]