Electrical Power and Energy

Electrical Power

Power is the rate at which electrical energy is transferred. For a component with current $I$ and potential difference $V$:

$P = IV$

Using $V = IR$ and $I = V/R$, two additional forms follow:

$P = I^2 R \qquad P = \frac{V^2}{R}$

Unit: watt (W), where 1 W = 1 J s⁻¹.

A 60 W lamp converts 60 J of electrical energy to light and heat every second.

Electrical Energy

Energy is power multiplied by time:

$E = Pt$

where $E$ is in joules (J), $P$ is in watts (W), and $t$ is in seconds (s).

In practice, the kilowatt-hour (kWh) is used for billing electricity:

$1 \text{kWh} = 1000 \text{W} \times 3600 \text{s} = 3.6 \times 10^6 \text{J} = 3.6 \text{MJ}$

Efficiency of Electrical Appliances

All appliances waste some energy, usually as heat. Efficiency is expressed as a percentage:

$\text{efficiency} = \frac{\text{useful power output}}{\text{total power input}} \times 100\%$

The LED lamp is more efficient than incandescent or fluorescent alternatives:

In the Caribbean, where electricity is expensive (imported fuel), LEDs offer significant cost savings.

Using the Power Formulas

FLASHCARD SET • 5 CARDSElectrical Power and Energy: Quick Recall