27. Resistors & DC Circuits

Power in Circuits

27. Resistors & DC Circuits

# Power in Circuits - Video Tutorials & Practice Problems

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### Power in Circuits

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2

Problem

ProblemA hair dryer operates at 120 V (the voltage produced by a household outlet), and outputs 1200 W of energy. For this problem, treat the hair dryer as a single resistor.

(a) At what current does the hair dryer operate?

(b) What is the resistance of the hair dryer?

A

(a) i=0.1 A;

(b) R=8.3×10

(b) R=8.3×10

^{−5}ΩB

(a) i=10 A;

(b) R=0.083 Ω

(b) R=0.083 Ω

C

(a) i=10 A;

(b) R=12 Ω

(b) R=12 Ω

D

(a) i=0.1 A;

(b) R=120,000 Ω

(b) R=120,000 Ω

3

Problem

ProblemAn incandescent lightbulb produces 100 W of light. If this lightbulb operates at 25% efficiency (meaning that out of all the power it generates, only 25% is released as light), what resistance must the lightbulb have if it operates at 120 V?

A

36 Ω

B

144 Ω

C

576 Ω

D

5.76 × 10

^{6}Ω## Do you want more practice?

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PRACTICE PROBLEMS AND ACTIVITIES (16)

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- Consider the circuit of Fig. E25.30. (b) What is the power output of the 16.0-V battery?
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- When a resistor with resistance R is connected to a 1.50-V flashlight battery, the resistor consumes 0.0625 W ...
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- A 1500-W electric heater is plugged into the outlet of a 120-V circuit that has a 20-A circuit breaker. You pl...
- The heating element of an electric dryer is rated at 4.1 kW when connected to a 240-V line. (b) What is the re...
- A 60 W lightbulb and a 100 W lightbulb are placed in the circuit shown in FIGURE EX28.9. Both bulbs are glowin...
- The five identical bulbs in FIGURE EX28.11 are all glowing. The battery is ideal. What is the order of brightn...
- A small toaster that operates at 120 V has a heating element made from a 4.4-m-long, 0.70-mm-diameter nichrome...
- The flash on a compact camera stores energy in a 120 μF capacitor that is charged to 220 V. When the flash is ...