Basic power calculation: how much current flows through a 60 W incandescent lamp operating from a 120 V supply (assume purely resistive behavior)?

Introduction / Context:
In household electrical calculations, determining current from known power and voltage is a foundational skill for sizing switches, fuses, and conductors. Incandescent lamps behave approximately as resistive loads at operating temperature, so the simple power law applies directly.

Given Data / Assumptions:

• Rated power P = 60 W.
• Supply voltage V = 120 V.
• Assume resistive load so P = V * I.

Concept / Approach:
For a resistive load, average power equals the product of RMS voltage and RMS current: P = V * I. Rearranging gives I = P / V. This relation is widely used for quick estimates in residential and commercial electrical design and safety checks.

Step-by-Step Solution:
Start from P = V * I.Solve for current: I = P / V.Substitute values: I = 60 / 120 = 0.5 A.Select 0.5 A.

Verification / Alternative check:
Compute the approximate resistance: R = V^2 / P = 120^2 / 60 = 240 Ω. Using I = V / R = 120 / 240 = 0.5 A confirms the same result, reinforcing consistency between formulas.

Why Other Options Are Wrong:
180 A and 7200 A are wildly unrealistic for a household lamp and would imply catastrophic faults. 2 A would correspond to a 240 W load at 120 V, not a 60 W bulb. “None” is wrong because 0.5 A is correct.

Common Pitfalls:
Confusing peak with RMS quantities; ignoring that real incandescent resistance varies with filament temperature (but nameplate power is rated at operating conditions, so the calculation remains valid).

Final Answer:
0.5 A