General Physics 2 Current & Resistance 1

Electric Currents (R)

General Physics 2 Current & Resistance 2

Resistors (L)

circuit symbol

what is the resistance of this resistor? Try some others.

General Physics 2 Current & Resistance 3

Electric Power (L)

• Power = Energy / time

Other usefulforms:

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Think-Pair-Share (L)

• You buy a 75-W lightbulb in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the US at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume that brightness is proportional to power consumed.]

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Think-Pair-Share (L)

• How many kWh of energy does a 550-W toaster use in the morning if it is in operation for a total of 15 min? At a cost of 9.0 cents/kWh, estimate how much this would add to your monthly electric bill if you made toast four mornings per week.

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Power in Household Circuits (L)

• Wires heat up at a rate equal to I2R (power)• fire hazard if I is too large• fuses prevent overloads by breaking circuit• short - two wires touching

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Fuses (L)

fuses that need tobe replaced

circuit breaker- breaks circuitwith a switch

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Household Circuits (L)

• What is the total current draw by these devices? If the circuit has a 20-A fuse, will the fuse blow?

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Alternating Current (L)

• DC • direct current• current is constant

• AC• alternating current• current varies like a sine wave• frequency usually 60 Hz (60

cycles per second)• Equations are valid when you

use RMS values

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Human Nervous System (L)

Messagestransmitted within nervous system are electrical signals passingalong the neuron

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Practice Problems

• Determine the equivalent resistance and the current through R1 for the circuits shown. Assume R1 = 10, R2 = 20 , and R1 = 30 , and the battery is 12 V.