Transcript 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’? + - 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