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Difficulty: MediumVoltage and Electromotive Force (EMF)

An avionics technician is testing a dual-polarity DC power supply that provides +12 V+12\text{ V} on the positive rail and −12 V-12\text{ V} on the negative rail, both measured relative to chassis ground. What is the total voltage (potential difference) across a component connected directly between the positive rail and the negative rail?

  1. A
    0 V0\text{ V}
  2. B
    12 V12\text{ V}
  3. 24 V24\text{ V}Answer
  4. D
    24 mV24\text{ mV}

Answer

24 V24\text{ V}
Voltage (electromotive force) is fundamentally a measure of electric potential difference between two specific points. By subtracting the negative rail potential (−12 V-12\text{ V}) from the positive rail potential (+12 V+12\text{ V}), the resulting potential difference is (+12 V)−(−12 V)=24 V(+12\text{ V}) - (-12\text{ V}) = 24\text{ V}.

Step-by-Step Solution

1
Identify the reference potentials of both supply rails relative to common ground
Vpositive=+12 VV_{\text{positive}} = +12\text{ V} and Vnegative=−12 VV_{\text{negative}} = -12\text{ V}
Voltage at any point in a circuit is defined with respect to a designated reference (chassis ground).
2
Calculate the potential difference across the load connected between the two rails
Vload=Vpositive−Vnegative=12 V−(−12 V)=24 VV_{\text{load}} = V_{\text{positive}} - V_{\text{negative}} = 12\text{ V} - (-12\text{ V}) = 24\text{ V}
Electromotive force / voltage across two terminals is the algebraic difference between their electric potentials.

Key Concept

Voltage as Electric Potential Difference
Estimated Time:45s
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Topics

Voltage and Electromotive Force (EMF)

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