Question

A bulb is stamped $40 \mathrm{~W} / 120 \mathrm{~V}$. What is its resistance when lighted by a $120-\mathrm{V}$ source?

   A bulb is stamped $40 \mathrm{~W} / 120 \mathrm{~V}$. What is its resistance when lighted by a $120-\mathrm{V}$ source?

Schaum’s Outline of College Physics

Schaum’s Outline of College Physics

Eugene Hecht 11th Edition

Chapter 27, Problem 12

Instant Answer

Solved by Expert Vishal Gupta

08/08/2021

Step 1

We can use the formula: Power (P) = Voltage (V) × Current (I) Rearranging the formula to find the current: I = P / V Now, we can plug in the given values: I = 40 W / 120 V = 1/3 A Show more…

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A bulb is stamped $40 \mathrm{~W} / 120 \mathrm{~V}$. What is its resistance when lighted by a $120-\mathrm{V}$ source?

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Key Concepts

Ohm's Law

Ohm's Law is a fundamental principle in electrical circuits that relates voltage, current, and resistance through the equation V = IR. It serves as a basis for understanding how electrical components behave when a voltage is applied, allowing for calculations of unknown quantities when two of the three parameters are known.

Power in Resistive Circuits

In circuits where the load is primarily resistive, electrical power can be expressed using the formulas P = I^2R and P = V^2/R. This relationship indicates how voltage and resistance determine the rate of energy consumption or conversion into heat in the resistor.

Resistance Calculation from Power Rating

The resistance of an electrical component can be computed from its power rating and operating voltage by rearranging the power formula to R = V^2/P. This concept is essential for designing circuits and ensuring that components meet desired electrical performance parameters.

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