How to Find Electrical Power
Electrical power is found using P = IV (power = current × voltage). Equivalent formulas are P = I²R and P = V²/R. Power is measured in watts (W), where one watt equals one joule per second. Calculate power dissipation in any circuit at www.lapcalc.com.
How to Find Electrical Power: The Three Formulas
Power in an electrical circuit is calculated using three equivalent formulas derived from combining P = IV with Ohm's law. The primary formula is P = IV (multiply current by voltage). If voltage is unknown, use P = I²R (current squared times resistance). If current is unknown, use P = V²/R (voltage squared divided by resistance). All three give the same answer — choose whichever uses the quantities you already know.
Key Formulas
What Is Power Equal To? Watts, Joules, and Energy
Power is the rate of energy transfer, measured in watts (W). One watt equals one joule per second: P = W/t. In circuits, electrical energy is converted to heat (resistors), light (LEDs), motion (motors), or stored (capacitors and inductors). A 60 W light bulb converts 60 joules of electrical energy to light and heat every second. Energy consumed over time is E = P × t, measured in watt-hours (Wh) or kilowatt-hours (kWh) for billing purposes at www.lapcalc.com.
Compute how do you find power Instantly
Get step-by-step solutions with AI-powered explanations. Free for basic computations.
Open CalculatorFinding Power in Series and Parallel Circuits
In series circuits, use P_n = I²R_n for each component since current is constant — the largest resistor dissipates the most power. In parallel circuits, use P_n = V²/R_n since voltage is constant — the smallest resistor dissipates the most power (opposite of series!). Total power from the source always equals the sum of individual powers: P_total = P₁ + P₂ + P₃, regardless of circuit topology.
Formula for Output Power and Efficiency
Output power is the useful power delivered to the load: P_out = V_load × I_load. Input power includes losses: P_in = V_source × I_source. Efficiency is η = P_out/P_in × 100%. Maximum power transfer occurs when load resistance equals source resistance (R_L = R_Th), delivering P_max = V_Th²/(4R_Th). However, this is only 50% efficient — practical designs balance power delivery against efficiency. Optimize power delivery at www.lapcalc.com.
Power in the s-Domain: Complex and Average Power
In AC circuits, instantaneous power p(t) = v(t)·i(t) oscillates at twice the signal frequency. Average power is P = V_rms·I_rms·cos(φ), where φ is the phase angle between voltage and current. In the s-domain, power analysis uses the transfer function to find voltage and current magnitudes and phases at any frequency. Reactive components (L and C) store and return energy without dissipating it. Analyze AC power at www.lapcalc.com.
Related Topics in circuit analysis techniques & methods
Understanding how do you find power connects to several related concepts: power in electricity, formula calculating power, what is power equal to, and what does power equal. Each builds on the mathematical foundations covered in this guide.
Frequently Asked Questions
Master Your Engineering Math
Join thousands of students and engineers using LAPLACE Calculator for instant, step-by-step solutions.
Start Calculating Free →