Examkin

Question

Difficulty: MediumOhm's Law Calculations and Concepts

An avionics technician tests a direct current (DC) relay control circuit connected to a 36 V36\text{ V} power supply. An in-line ammeter indicates that the relay coil draws a steady current of 75 mA75\text{ mA}. What is the total electrical resistance of the relay coil?

  1. A
    0.48 Ω0.48\text{ }\Omega
  2. 480 Ω480\text{ }\OmegaAnswer
  3. C
    2.7 Ω2.7\text{ }\Omega
  4. D
    2,700 Ω2,700\text{ }\Omega

Answer

The total electrical resistance of the relay coil is 480 Ω480\text{ }\Omega.
According to Ohm's Law, resistance is determined by dividing voltage by current (R=VIR = \frac{V}{I}). First, converting the current from milliamperes to amperes gives 75 mA=0.075 A75\text{ mA} = 0.075\text{ A}. Dividing the 36 V36\text{ V} supply by 0.075 A0.075\text{ A} yields a resistance of 480 Ω480\text{ }\Omega.

Step-by-Step Solution

1
Convert the measured current from milliamperes to base amperes.
I=75 mA=75×10−3 A=0.075 AI = 75\text{ mA} = 75 \times 10^{-3}\text{ A} = 0.075\text{ A}
Standard electrical calculations using Ohm's law require values to be expressed in base SI units (volts, amperes, and ohms).
2
Apply Ohm's law rearranged to solve for resistance (R=VIR = \frac{V}{I}).
R=36 V0.075 A=480 ΩR = \frac{36\text{ V}}{0.075\text{ A}} = 480\text{ }\Omega
Resistance equals electromotive force (voltage) divided by current flow.

Key Concept

Calculating resistance in a DC circuit using Ohm's Law with metric prefix conversion.
Estimated Time:1m 0s
Rate this question

Topics

Ohm's Law Calculations and Concepts

More questions from this topic