Do Now

• Describe what you think happens electrically when you dim a light

Circuits and Ohm’s Law

The Circuit• Remember from our lightning lesson: electricity needs a

complete path to travel• Another term for a path is a circuit• Every circuit consists of a power source and some load

The Circuit• Electrons flow from the negative terminal, through the load,

to the positive terminal• Those flowing electrons are what powers the light• What’s another name for ‘flowing electrons’?

+ -

Think-Pair-Share• Brainstorm different ‘loads’ that you can attach to your circuit,

besides an electric light

The Circuit• What happens if you remove one of the wires? Will any of the

lights stay lit? Why or why not? • This process is also known as a ‘switch’.

Circuit building!• Using your battery as the power source, and your motor as

your load, build a circuit which makes your motor run• Bonus circuit: try adding a light to your circuit which doesn’t

turn off when you disconnect the motor

Parallel vs. Series• Series• Negative terminal of

one bulb connected to the positive terminal of the other

• Parallel• Positive terminal

connected to positive, negative to negative

+ - + -

+ -

+ -

V=IR• V=IR, or Ohm’s Law is a very important formula in electronics• V – voltage –the pressure on the electrons which causes them

to move through the circuit• I – current – the actual number of electrons moving through

the circuit• R – resistance – how much of the electrical current is ‘resisted’

or ‘used up’• Any load has a certain amount of resistance

V=IR• If I have a very high-resistance load attached to a 9V battery, is

the current high or low?

• If I have a very low-resistance load attached to a 9V battery, is the current high or low?

Potentiometer• Most electrical components have one resistance which never

changes (light bulbs, motors, etc.)

• A potentiometer is a resistor which lets you vary how much resistance it has

• What happens to the speed of your motor when you have a low-resistance potentiometer in series with the motor?

• What happens to the speed of your motor when you have a high-resistance potentiometer in series with the motor?

Circuit building!• Using your battery, potentiometer, and motor, build a series

circuit which lets you vary the speed of the motor

Measure the voltage• Using your multimeter, measure how many volts are across

your motor when it’s all the way on• Using your multimeter, measure how many volts are across

your motor when it’s all the way off

• The higher the potentiometer’s resistance is, the more power it consumes, leaving less for the motor

Questions?

Exit Ticket

•Describe what is going on at the circuit level when we dim the lights