Understanding electrical power consumption and energy storage
Power is the rate at which electrical energy is transferred or converted. It measures how much energy is used per unit time.
P = V × I
where:
P = I² × R (using Ohm's Law)
P = V² / R (using Ohm's Law)
All three formulas are equivalent and derived from P = V × I and V = I × R
Energy is the total amount of work done by electricity over time. It's measured in Joules (J) or kilowatt-hours (kWh) for practical applications.
E = P × t
where:
A red LED runs at 2V with 20mA current. Calculate the power:
P = V × I = 2V × 0.02A = 0.04W = 40mW
A 220Ω resistor with 10mA current. Find power dissipation:
P = I² × R = (0.01A)² × 220Ω = 0.022W = 22mW
A 60W light bulb runs for 5 hours. Calculate energy used:
E = P × t = 60W × 5h = 300Wh = 0.3kWh
At $0.12/kWh, this costs: 0.3 × $0.12 = $0.036 (about 4 cents)
Every component has a maximum power rating. Exceeding this causes overheating and component failure.
Safety Rule: Always ensure components operate well below their maximum power rating (typically 50-70% max) to prevent overheating and extend component life.