Power & Energy in Circuits
Power is the rate of energy transfer. In circuits, components either supply power (sources) or absorb power (loads).
Power Formulas
Power Calculation
Medium
A 60W light bulb operates at 120V. What is its resistance and current?
1
Find current
P = VI → I = P/V = 60/120 = 0.5 A
2
Find resistance
R = V/I = 120/0.5 = 240Ω
Or: R = V²/P = 14400/60 = 240Ω
Answer:
I = 0.5 A, R = 240Ω
Key Takeaways
P = VI = I²R = V²/R
Resistors always absorb (dissipate) power
Power is measured in Watts