Circuits-More Complicated Circuits

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