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Difficulty: MediumOhm's Law

A shipboard auxiliary alarm horn is connected across a 72 V72\text{ V} direct-current (DC) power rail. When activated, the horn draws a steady current of 120 mA120\text{ mA}. Based on Ohm's Law, what is the total electrical resistance of the horn circuit in ohms (Ω\Omega)?

Answer: 600 Ω

Answer

The total electrical resistance of the horn circuit is 600 Ω600\ \Omega.
According to Ohm's Law, resistance equals voltage divided by current (R=VIR = \frac{V}{I}). Converting 120 mA120\text{ mA} to standard amperes gives 0.12 A0.12\text{ A}. Dividing 72 V72\text{ V} by 0.12 A0.12\text{ A} yields an electrical resistance of 600 Ω600\ \Omega.

Step-by-Step Solution

1
Convert the current measurement from milliamperes to base amperes.
I=120 mA=0.12 AI = 120\text{ mA} = 0.12\text{ A}
Ohm's Law requires standard SI units (volts, amperes, and ohms) for direct substitution.
2
Rearrange Ohm's Law (V=I×RV = I \times R) to isolate resistance (RR).
R=VIR = \frac{V}{I}
The unknown quantity in this circuit problem is resistance.
3
Divide the applied voltage by the circuit current.
R=72 V0.12 A=600 ΩR = \frac{72\text{ V}}{0.12\text{ A}} = 600\ \Omega
Evaluating the division yields the equivalent circuit resistance in ohms.

Key Concept

Ohm's Law defines the proportional relationship between voltage, current, and resistance (R=VIR = \frac{V}{I}).
Estimated Time:45s
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Topics

Ohm's Law

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