Power Formula

Power Formula

Kilowatt Hours

• The electric company charges you for the amount of electrical energy you use.

  • Electrical energy used is measured​ in kilowatt hours (kWh).

• Despite the name, it doesn't mean the number of kilowatts you're using per hour.​

  • 1 kilowatt hour is the amount of energy you’d use if you kept a 1,000 watt appliance running for an hour.​

​

• Charge flow reverses direction periodically

• Due to the way that power plants generate power

• AC in a simple circuit​

Alternating Current

Periodicity

• Voltage, current, and power fluctuate with time

• So we usually talk about the averages ​

Average Power

Root Mean Square (rms)

USA conventions

• V₀ = 170 V

• V_rms = 120 V

• Most electronics in the U.S. specify 120 V, so they really mean V_rms

• We will always (unless otherwise noted) use average power, and root mean square current and voltage

• As as result, all of the previous equations work!​

Resistance