Circuits

James Joule

proposed a connection between the work a motor does and the heat it produces

Joules

units of energy

William Thomson

aka Lord Kelvin; quantified Joules’ ideas into the laws of thermodynamics

Conservation of energy

total amount of energy in a closed system always remains the same; energy cannot be created or destroyed

Kinetic energy

energy something has when it is moving

Heat

energy in transit between objects that are at different temperatures; the combined kinetic energy exchange between all the atoms in two substances in contact with each other

Phlogiston

a substance that was once theorized to make up heat, not actually a thing; heat is a property already inherent in materials

Temperature

average kinetic energy of the atoms of a substance

Second Law of Thermodynamics

heat flows from high-temperature objects to low-temperature objects

Third Law of Thermodynamics

no substance can ever actually reach absolute zero; to cool a substance down to absolute zero, you would need a substance lower than zero, which doesn’t exist

Gravitational potential energy

energy that an object posses due to its position in a gravitational field

Potential energy

energy that can readily turn into kinetic energy

Electric potential energy

works the same way as gravitational potential energy but via the electric force; directly proportional to an object’s charge

Voltage

difference in electric potential, a way of describing how the electric field changes across some distance

Electric potential

electric potential energy of an object divided by its charge

Volts

units for electric potential; joules per coulomb

Equipotential lines

lines that indicate electric potential; the closer they are, the stronger the electric field is

Change in kinetic energy of a charged particle

∆E=q*V

Alessandro Volta

inventor of what is the closest thing to a modern battery; theorized that electricity came from the metals in the Galvanis’ experiment, not the frog

Battery

term used by Franklin to refer to multiple Leyden jars connected together

Piles

word used before battery to describe multiple Leyden jars connected together

Lucia and Luigi Galvani

discovered that the bodies of dead frogs jolted when touched with two different metals, theorized that this was due to the electricity within the bodies

Galvanism

potential scientific explanation for the mysterious life force

Truth of the Galvanis’ experiment

the acids in the frog’s skin dissolved the metals, stealing electrons from one and giving electrons to the other

Giovanni Aldini

nephew of the Galvanis, showed that the left hemisphere of the brain controls the right side of the body and vice versa and that electroshock therapy can potentially treat depression

Battery (modern)

any device that maintains a constant voltage by keeping two collections of positive and negative charge separate from each other

Disposable batteries

uses two rods of Zn and C submerged in sulfuric acid, which dissolves the Zn, making it negatively charged, and polarizes the C rod, making it positively charged outside the acid; aka primary cells

Terminal

parts of the battery rods that are outside of the acid; will continue to recharge due to the acid until the zinc rod is fully dissolved

Secondary cells

batteries that can be recharged

Lithium-ion batteries

moves lithium ions through a conducting chemical fluid, switches terminals when charging, allowing it to be reused; used inmost electronic devices

Circuit

closed loop that allows electricity to continually flow

Direct current

current that always flows in the same direction

Electromotive force

used to refer to the voltage of a circuit

Electric current

quantified by measuring the amount of charge that flows past a point per second

Amperes

unit for current; coulombs per second; named after Andre-Marie Ampere

Electric force

fundamental force by which atoms communicate with each other

Electrocardiogram (EKG)

device that measures voltage across various parts of the body to measure a person’s heartbeat; visual output measures voltage versus time

Electronic pacemaker

device that routinely sends electrical pulses to maintain a heart’s constant rhythm

Electrophysiology

study of electricity of the human body

Ohm’s Law

way to measure a current; I=V/R

Resistance

quantity that resists the flow of current, measured in ohms (Ω); form of friction that charged particles experience as they flow through a circuit

Factors that affect resistance

conductive materials have low resistance, longer wire will have greater resistance, higher temperature causes greater resistance

Ohmic circuits

circuits that obey Ohm’s Law

Danger of voltage and current

large voltage causes charge to build up a lot of energy, but if very few charged particles move through that potential, very little energy is delivered; large voltage is only dangerous with high conductivity

Relationship between voltage and current

voltage creates the conditions for current, current is what actually affects you

Power

rate of energy change over time, measured in watts

Watt

one joule per second

Electron flow through wire

encounters friction which creates heat in the wire

Incandescent lightbulbs

tungsten filament inside heats up enough to glow yellow (2000 C)

Kilowatt-hour

3.6 million joules

Drift velocity of electrons

less than 1 mm/s; electrons are actually moving millions of meters per second, but they move randomly and bounce off each other so they don’t get very far

Power plants

when a switch is flipped, it sends a signal to the wires in your home to start moving; switches on an electric field to accelerate the electrons

Electron movement

when an electron moves, its electric field shifts, telling other electrons where it is and repelling them; information on electron position spreads at the speed of light

Proton movement

do not move around as much as electrons, but will jiggle more when electrons are flowing, increasing temperature

Superconductors

substances for which there is a point at which resistance becomes zero; used in machines requiring high currents; require extremely low temperatures

Resistor

resists current by taking energy away from the flow of the charge and turning it into another form of energy

Switch

allows current to run through it when it is closed, breaks circuit when it is open

Series circuit

two resistors are in series, same current runs through both of them, greater resistance, reduced current

Resistance in series circuits

R_total=R₁+R₂+R₃+…; increases as number of resistors increases

Parallel circuit

two resistors are in parallel, current has two different paths it can take, more current flows through the resistor with lower resistance

Resistance in parallel circuits

1/R_total=(1/R₁)+(1/R₂)+(1/R₃)+…; decreases as number of resistors increases

Advantage of parallel circuits

one element of a circuit can be removed without disrupting the current flowing through the other parts

Fuse

bit of wire made of a material with a low melting point; melts if the current gets too high

Circuit breaker

peace of metal that expands and breaks a circuit if it is heated too much

Relationship between power and current

P=IV

Grounding

high-powered devices include a third prong that is directly connected to the ground (which has a lower potential), so that if the appliance becomes charged, the current flows into the prong, not people

Capacitor

any two conductors separated by some small distance

Leyden jar

early form of a capacitor, has metal foil inside and outside separated by glass, metal rod is inserted into jar to connect to inner foil

Capacitor vs. Battery

capacitor has no way to maintain voltage if current has a way to flow from one end to the; if ends of a charged capacitor are connected, the separated charges will neutralize each other

Uses of capacitors

used in situations that require a quick, temporary flow of current; camera flash, temporarily data storage in RAM, backup energy source, computer keys, touch screens

Capacitance

quality that determines how much charge a capacitor can store, based on physical properties like size of conductors and the distance between them

Dielectric

material put between two conductors in a capacitor, affect the amount of charge a capacitor can store; becomes polarized when conductors become charged, has electric field that points in opposite direction of capacitor’s

Dielectric breakdown

when a dielectric becomes a conductor; large excess charge→ very large voltage + very strong electric field→ electrons can go through dielectric; threshold for air is 3 Megavolts

Lightning

turbulence in clouds cause the charges in them to separate (bottom is -, top is +), polarizing the ground (+); if voltage becomes high enough, air between cloud + ground can conduct electricity

Thunder

sonic boom caused by rapid expansion of air as it heats up

Lightning Safety Tips

be indoors or away from tall objects, keep feet close together to decrease potential diff between them and minimize current flowing through you, crouch down, don’t hold up metal objects

Transient Luminous Events

phenomena caused by charge separation in storm clouds

Lightning on other Planets

thicker atmosphere of Venus causes more frequent lightning, Jupiter is entirely atmosphere which causes more powerful lightning, there is even lightning on Saturn’s moon Titan