Download V=IR

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’?
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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
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• Parallel
• Positive terminal
connected to
positive, negative to
negative
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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