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:
General Physics 2 Current & Resistance 4
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.]
General Physics 2 Current & Resistance 5
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.
General Physics 2 Current & Resistance 6
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
General Physics 2 Current & Resistance 7
Fuses (L)
fuses that need tobe replaced
circuit breaker- breaks circuitwith a switch
General Physics 2 Current & Resistance 8
Household Circuits (L)
• What is the total current draw by these devices? If the circuit has a 20-A fuse, will the fuse blow?
General Physics 2 Current & Resistance 9
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
General Physics 2 Current & Resistance 10
Human Nervous System (L)
Messagestransmitted within nervous system are electrical signals passingalong the neuron
General Physics 2 Circuits 11
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.