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Ohm’s Law and Power Notes
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• An electric circuit is a complete path through which electric current travels.
• A good example of a circuit is the one found in an electric toaster.
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• Current only flows when there is a complete and unbroken path, or a closed circuit.
• Flipping a switch to the “off” position creates an open circuit by making a break in the wire.
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Voltage and Current • Voltage is the energy which causes electrical
energy to flow. Current flows from higher voltage to lower voltage.
• Current is what actually flows (the electrons) and does work (lights a light bulb, turns a blade in a blender, heats a coil).
• You cannot have current without voltage but you can have voltage without current!
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Resistance • Resistance
controls how much current flows for a given voltage.
• When resistance is low, current flows easily.
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8.2 Resistance • Any object that uses
electricity has resistance! (for example: light bulbs)
• Electrical resistance is
measured in ohms.
This light bulb has a resistance of 1 ohm.
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• Light bulb: 240 ohms.
• Dry skin has higher resistance, wet skin has lower resistance.
• Conductors have lower resistances, insulators have higher resistances.
Resistance of Common Objects
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What 5 changes could you make to a closed circuit consisting of a battery, a light bulb, and a switch that would increase the amount of current?
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1. You could increase the number of batteries, which would increase total voltage
2. You could replace the light bulb with one that had a lower resistance
3-5. You could use thicker wires, shorter wires, wires made from a material with higher conductivity.
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• Voltage and current are directly proportional
• Doubling the voltage doubles the current.
• Resistance and current are inversely proportional.
• Doubling the resistance cuts the current in half.
• If you know two of the three quantities, you can use Ohm’s law to find the third.
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Ohm’s law
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Electrical Power • Electrical power measures how much
energy (current and voltage) is used in electrical devices. Measured in watts.