Question 1

What is electrical power?

Accepted Answer

Electrical power is the rate at which electrical energy is transferred in a circuit, measured in Watts (W). One Watt equals one Joule per second. It is calculated as P = IV (voltage times current). A 100 W light bulb converts 100 joules of electrical energy into light and heat every second.

Question 2

What is the relationship between watts, volts, and amps?

Accepted Answer

Power (watts) = Voltage (volts) × Current (amps). If you know any two of these three quantities, you can calculate the third. For example, a device drawing 2 A from a 120 V outlet uses 240 W of power. This is the most fundamental equation in electrical engineering.

Question 3

How do I calculate electricity cost?

Accepted Answer

Electricity is billed in kilowatt-hours (kWh). Multiply the power in kilowatts by the number of hours of use, then multiply by your rate per kWh. For example, a 100 W device running 24 hours uses 2.4 kWh. At $0.12/kWh, that costs about $0.29 per day or $8.64 per month.

Question 4

Why does P = I²R give the same result as P = V²/R?

Accepted Answer

Both are derived from P = IV combined with Ohm's Law (V = IR). Substituting V = IR into P = IV gives P = I²R. Substituting I = V/R into P = IV gives P = V²/R. All three formulas are equivalent and give the same power, just using different combinations of the known quantities.

Electrical Power Calculator (P = IV)

Frequently Asked Questions