Energy Consumption and Work
Electrical power ($P$) is the rate at which electrical energy is converted into another form of energy, such as heat, light, or mechanical motion. In the SI system, power is measured in Watts ($W$), where $1 , \text{Watt} = 1 , \text{Joule per second}$.
Understanding the Triple Relationship
Power can be calculated using any two of the three main electrical variables:
- Voltage & Current ($P = V \cdot I$): This is the most direct measure. It shows that power is the product of electrical pressure and flow.
- Current & Resistance ($P = I^2 \cdot R$): Often used to calculate "I-squared-R losses," which is the power wasted as heat in wires.
- Voltage & Resistance ($P = V^2 / R$): Useful for determining how much power a device (like a heater) will draw when plugged into a fixed voltage source (like a $120 , \text{V}$ wall outlet).
The Formula
Where:
P=
Power (Watts, W)V=
Voltage (Volts, V)I=
Current (Amperes, A)R=
Resistance (Ohms, Ω)Example Calculation
An electric heater with a resistance of $10 , \Omega$ is plugged into a $120 , \text{V}$ outlet.
- Use Power-Voltage-Resistance Formula ($V^2 / R$): $120^2 / 10 = 14,400 / 10 = 1,440 , \text{Watts}$.
The heater consumes $1.44 , \text{kW}$ of power.