Summary

• Electric current
• Conductivity & resistivity
• Ohm's law

Today's joke




• Written Quiz Ch. 25



• Electric power
• calculation
• Ohm's law and power applet
• electric power transmission
Example #1
Example #2
Example #3




• The cost of electricity
Example #4

POP4 21.15
If a 1500-hp generator is 80% efficient at converting mechanical energy into electrical energy, what current does it deliver at a terminal voltage of 2000 V?
A. 0.600 A
B. 125 A
C. 280 A
D. 448 A
Answer















PSE6 27.50
How much time does it take a 120 V, 2.00 A coffee maker to heat 0.500 kg of water from 23°C to 100°C?
A. 67.2 sec
B. 7.55 min
C. 11.2 min
D. 38 min
Answer















PSE10 27.04c
A 75-W @ 120-V lamp is connected to an extension cord with two wires of 0.800 Ω each. What power is actually delivered to the lamp?
A. 75.0 W
B. 74.5 W
C. 73.8 W
D. 72.2 W
Answer















PSE6 27.51
About how much does it cost to use a 700-watt coffee maker every morning for a year? Assume electricity costs about $0.10/kWh.
A. $1
B. $10
C. $100
D. $1000
Answer



























 



D. 448 A






















 



C. 11.2 min






















 



C. 73.8 W






















 
B. $10



This assumes you run the coffee maker for 20 minutes every morning and the price is $0.10 /kWh.