What is the formula for determining the amperage or wattage load?

• A. W=V x A
• B. W=V/A
• C. W=A/V
• D. W=V^2

Answer: (A)

Power in an electrical circuit is calculated as the product of voltage and current. So the wattage load equals voltage times amperage. In symbols, watts = volts × amperes. This means you determine load by multiplying the circuit’s voltage by the current drawn by the device. If you know wattage and voltage, you can find current as I = P / V, and if you know wattage and current, you can find voltage as V = P / I. The other expressions aren’t correct in general: dividing voltage by current wouldn’t give watts, and W = V^2 omits the current or resistance term needed (except in a specific case with known resistance, where P = V^2 / R).