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Power, Current & Energy

Power, Current & Energy. Circuits with unknown emf (voltage) and unknown resistance. Power. P=IV=I 2 R=V 2 / R Energy = (P)(t) Power in kW, time in hours, energy in kW-h. Power in W, time in seconds, energy in J.

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Power, Current & Energy

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  1. Power, Current & Energy Circuits with unknown emf (voltage) and unknown resistance

  2. Power • P=IV=I2R=V2/R • Energy = (P)(t) Power in kW, time in hours, energy in kW-h. Power in W, time in seconds, energy in J. To find the cost of energy, just multiply the cost per kW-h times the # of kW-h used.

  3. Example #1 A blow dryer is rated at 1600Watts. It is plugged into an outlet which provides 120V. a. What is the current running through the dryer? b. How much energy is used in 20 minutes of blow drying? c. If electricity costs $0.15 per kW-h, what is the cost of operating the blow dryer?

  4. Example #2The circuit shown has 3 amps going through the 5W resistor. a. What is the equivalent resistance? b. What is the total current in the circuit? c. What is the voltage (emf) of the battery?

  5. Example #3In the circuit, the total current is 1 amp. The power rating in R2 is 9 watts. a. What is the reading on the voltmeter? b. What are the resistances of R2 and R1?

  6. Example #4The current in the 8W resistor is 4 amps. a. Find the current in the other resistors. b. What is the voltage (emf) of the battery?

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