Electric Current

What did we just finish studying? _________: the buildup of electric charges on objects.

What are we studying next? ___________: the flow of charges along a conductor.

I = ________ unit: _____

q = ________ unit: _____

t = _______ unit: ______

What makes the charges want to flow anyway? __________: aka ______ _______. A difference in the voltage at each end of a wire (“across” the wire)

10V e- 0V

t

qI

IRV

Current (Definition formula): how fast do the charges flow?

It’s work to go that way!

So, charges flow because of potential difference (the energy to escape crowded electron areas) What determines how fast they flow?

1.The size of the voltage difference.

•1V: e-

•10,000V: e-

2. Resistance: obstacles in their path

•Wire thickness. Thin = _____

•Wire temperature. Hot = _____

•Wire material conductivity. Good conductor =_____

•Wire length. Long = ______

I could use some time alone.

@#$%! Get me out of here!.

Ohm’s Law: (Relationship formula.)

Rearranging to is more meaningful, but it’s usually written V=IR

Ohm’s law means: Current is directly related to voltage: (more push, more flow) but indirectly related to resistance (more difficult path, less flow).

V = _______ unit______

I= _______ unit:_______

R= _______unit:_______

How much current flows through a circuit with 8 ohms of resistance and a potential difference of 120V?

R

VI

V = IR

Electrical Power: It was a dark and stormy night. Lightning flashes. The lights go black. ‘Oh no!’’ you cry, ‘the power is out!’

What is (electrical) power anyway? It’s the energy per second supplied when there is a current.

How does electrical energy travel?

• Way faster than the electrons do (nearly speed of light vs. cm/min)

• As a wave in the electric and magnetic fields around the charges

• Outside the wires

Power and circuits

Power Plants and $:

Georgia Power charges you how much? About ________.

What is a kWh? A unit of __________ equal to you, using

__________ for _________

C= _________ unit_______

r= _________ unit________

P= _________ unit_______

t= __________ unit_______You left your 350 W TV on all night from 4 p.m. to 8:30 a.m. Your mother tells you to pay for the power it used. Your power costs $0.10/kWh. How much will it be?

Circuits: a closed path made up of wires, a “pump” and

resistors.

•Pump = source of voltage: “cells,” batteries, generator, power plant

•Resistor = thing using electricity: lamp, TV, dryer

•DC current: Electrons move from + terminal to – terminal (what we think of as normal =batteries)

•AC current: Electrons dance back and forth and don’t progress forward (electricity from the wall)

•Energy moves from the pump to the resistor outside the wires in both directions as a wave in the electric field.

Series Circuits• only one path for the current to flow through• if one resistor burns out, the entire circuit is “open” and stops working. • same current through every resistor

Parallel Circuits: • more than one path for current to flow through• if one resistor burns out, only one path is “open” so circuit still works• same voltage across every resistor

Power: amount of energy transmitted over time.

Definition formula: P= ____________unit: ___

Energy:________ unit:____

t= _________ unit:____

Relationship formulas: power is related to current, resistance and voltage, which gives us three new formulas!

Your hair dryer uses 5 amperes when on the high setting. Its resistance is 24 ohms. How much power does your hair dryer draw?

t

EnergyP

R

VRIIVP

22

rPtC

Circuit Schematics and Ohm’s Law Charts:

Draw a circuit with:

•9V battery

•R1 = 5Ω

I = ____A

Rules:

•Battery (multiple “cells”) is labeled with the V, is on left, + line is long and on top, - line is short and down.

•Wires in rectangle shape

•Resistor is a zigzag, labeled R1 = ___Ω

Draw a series circuit and Ohm’s law chart for:

•9V battery

•2 resistors in series, 5Ω and 13 Ω

More Rules:

• resistors in series make one path.

•In series: Current is the same!

•Label R1, R2 etc.

•Fill in chart using V=IR for and series formulas for

Draw a parallel circuit an Ohm’s law chart for:

•9V battery

•2 resistors in parallel, 5Ω and 13 Ω

•1 fuse for _______ A

More Rules:

• resistors in parallel make many paths

•In parallel: Voltage is the same!

•Fill in chart using V=IR for and series formulas for

•Fuse symbol is .You decide current from chart

Draw a series circuit an Ohm’s law chart for:

•12V battery

•Series: R1= 6Ω, R2=3 Ω

•1 breaker for ______ A

•Voltmeter around R1

•Ammeter

More Rules:

• Breaker symbol is

•Voltmeter symbol is . It measures _______ difference. Wire voltmeters in __________ around the resistor because it measures the difference.

•Ammeter symbol is . Ammeters measure ________. Wire is ________ with the circuit because it measures electron flow.