When should I use P = V²/R versus P = I²R?

Both formulas are correct but optimal in different situations:

Use P = V²/R when:

• You know voltage and resistance
• Voltage is constant (like a fixed power supply)
• You're analyzing parallel circuits
• Resistance changes and you need to see power impact

Use P = I²R when:

• You know current and resistance
• Current is constant (like series circuits)
• You're calculating power loss in wires
• You're analyzing heat dissipation

Example scenario: A 10Ω resistor in a circuit:

• If voltage is known (12V): P = 144/10 = 14.4W
• If current is known (1.2A): P = 1.44 × 10 = 14.4W

Both give the same answer—choose based on what you can measure easily.