Electric Power

R

VRIIVP

22

Example: Electric Heater

An electric heater draws 15.0 A on a 120-V line. How much power does it use and how much does it cost per month (30 days) if it operates 3.0 h per day and the electric company charges 10.5 cents per kWh? (For simplicity, assume current flowing in one direction).

Lightning Bolt

Typical lightning bolt can transfer 109 J of energy across a potential difference of perhaps 5x107 V during a time interval of about 0.2 s. Use this information to estimate the total amount of charge transferred, the current, and the average power over the 0.2 s.

Power in Household Circuits

Will a Fuse Blow?

Define the total current drawn by all devices in the circuit shown in the next slide.

Alternating Current

ftRIRIP

ftR

V

R

VI

ftVV

2sin

2sin

2sin

220

2

0

0

Average Power

R

VP

RIP

20

20

2

1

2

1

Root-Mean-Square Values (RMS)

002

002

707.02

707.02

VV

VV

II

II

rms

rms

Stereo Power

Each channel of stereo receiver is capable of an average power output of 100 W into a 8- loudspeaker. What is the rms voltage and rms current fed to the speaker at the maximum power of 100 W?