Bell Ringer

Bell Ringer

You walk up to your friend to give him a high-five for acing his science test. To your surprise, you shock him instead. Why did this happen?

NOTES: Current ElectricStatic vs CurrentVoltage, Resistance, and CurrentOhm’s Law

Agenda

Current ElectricityCurrent electricity is a steady flow of

electrons. Unlike static, current is always moving.

There are 3 characteristics of current electricity:VoltageCurrentResistance

Voltage (Potential Difference)

The PUSH that makes electrons flow (electrons have potential to flow but won’t on their own)

A difference between energy levels is needed for flow• Electrons flow in a circuit when there is an

energy difference from one end of the energy source to the other end of the energy source (like a battery)

Units = VOLTS (V) 1 Volt = 1 Joule/Coulomb

Symbol = V (capital)

Pop Bottle Demo

Draw a picture and write a description of the demo with the pop bottles for voltage.

Electric CurrentThe FLOW of electric charges in a circuitUnits = Amperes (amps)

1 amp = 1 C/s (1 Coulomb of charge moving past a point in 1 second)

Symbol = ISpeed of Current is affected by

• Type, length, & thickness of wire• Voltage

When Voltage , Current

Pop Bottle Demo

Draw a picture and write a description of the demo with the pop bottles for current.

2 Types of CurrentThere are 2 types of electrical

currentsDC = Direct CurrentAC = Alternating Current

DC electricityDirect current means that

the electrons flow in only one direction.

This is the kind of electricity produced by a battery

Electrons come out of the negative end and flow back into the positive end.

AC electricityAlternating Current electricity means that

the direction of electron flow flips back and forth

This is the kind of electricity produced by spinning a generator.

The electricity in homes in the United States changes direction 60 times a second!

ResistanceOpposition to the flow of electronsUnit = Ohm (Ω)Symbol = R

• Highest resistance in:Poor conductors Thin wiresLong wires

Ohm’s Law

V = I ● RVoltage (volts, V) Current

(amps, A)

Resistance(ohms, Ω)

•Relates Electric Current, Voltage, & Resistance

Practice Problem 1

Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it.

V = ___________

I = ____________

R = ___________

V = I ● RV = 0.5 amps x 3 ohm’sV = 1.5 volts

?0.5 amps

3 Ω (ohm’s)

Practice Problem 2

A radio with a resistance of 240 Ω is plugged into a 120 V outlet. What is the current flowing through the outlet?

V = I ● R120 V = I ● 240 ΩI = 120 V

240 Ω

120 V

?240 Ω

I = 0.5 amps

V = ___________

I = ____________

R = ___________

Practice Problem 3

Find the resistance of a circuit that draws 0.06 amps with 12 volts applied.

V = ___________

I = ____________

R = ___________

V = I ● R12 v = 0.06 amps ● RR = 12 V

0.06 amps

12 V

0.06 amps

?

R = 200 Ω

Assignments

Review questions and Ohm’s Law calculations