http://phet.colorado.edu/new/simulations/sims.php?sim

=Ohms_Law

Voltage (Volts)

Current (Amps) Resistanc

e (Ohms or Ω)

What is the voltage of this

battery?

4.5 V4.5 V

Find the amount of resistance in Find the amount of resistance in a toaster oven that has a voltage a toaster oven that has a voltage of 120 V and has 3 amps of of 120 V and has 3 amps of current running through it.current running through it.

I = V/RI = V/R3amps = 120V/R3amps = 120V/RR = 40 R = 40 ΩΩ

Find the Find the voltage dropvoltage drop across across eacheach light bulb in the circuit light bulb in the circuit belowbelow

10 V

1 Ω

1 Ω

1 Ω 1 Ω

1 Ω

2 V2 V

Voltage will drop with each Voltage will drop with each resistor.resistor.

The voltage will always drop to The voltage will always drop to 0V in the end.0V in the end.

10 V

2 Ω

2 Ω

2 Ω 2 Ω

2 Ω

You must You must ADDADD the the values of values of ALLALL resistors to resistors to find the find the totaltotal resistanceresistance for the for the circuit before you use circuit before you use Ohm’s LawOhm’s Law

RRT T = R= R1 1 + R+ R2 2 + R+ R3..3..

Your Turn…Your Turn… Find the amount of current in the Find the amount of current in the

circuit below circuit below

10 V

2 Ω

2 Ω

2 Ω 2 Ω

2 Ω

I = V/RI = V/RTT I = 1 ampI = 1 amp

What is What is the the

current current in each in each

resistor?resistor?

I = V/RI = V/RTT

I = 9 / 3I = 9 / 3

I = 3 I = 3 ampsamps

For a parallel circuit, voltage drop For a parallel circuit, voltage drop over each resistor equals the over each resistor equals the

total starting voltagetotal starting voltage

12 V3 Ω 3 Ω3 Ω3 Ω

Practice!!Practice!! What is the What is the voltage dropvoltage drop over over

eacheach light bulb? light bulb? What is the What is the currentcurrent over over eacheach??

12 V3 Ω 3 Ω3 Ω3 Ω

12 V12 V4 4 ampsamps

In a parallel circuit, there In a parallel circuit, there are several paths for are several paths for electrons to flowelectrons to flow

SO……..SO……..The current is divided The current is divided equallyequally among among each each branch branch of a parallel circuitof a parallel circuit

Electrical PowerElectrical Power

P = IVP = IVPower (Watts)

Current (Amps)

Voltage (Volts)

Electric Electric CompaniesCompanies

We pay for We pay for electrical electrical energy by the energy by the kilowatt-kilowatt-hourhour

Remember….. Remember….. 1 1 KiloKilowatt = watt = 10001000 watts watts

Def: Devices Def: Devices that measure that measure or react to or react to specific levels specific levels of current of current

Examples……Examples…… Safety Switches and Ground Fault Circuit Interrupters (GFCIs) designed to stop the flow of too much electricity

Examples……Examples…… FuseFuse: : contains

a small piece of metal that melts if the current becomes too high, opening the circuit (must be replaced).

Examples……Examples……

Circuit Breaker:Circuit Breaker: contains a piece of metal that bends when it gets hot, causing a switch to open the circuit (can be switched back on).