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Difficulty: MediumDirect Current (DC) vs. Alternating Current (AC)

Electric utility companies distribute power across regional power grids using high-voltage alternating current (AC) rather than direct current (DC). Which of the following best explains why alternating current is preferred for long-distance power distribution?

  1. A
    Alternating current maintains a continuous, unidirectional electron flow that completely eliminates heat dissipation in transmission cables.
  2. B
    Alternating current allows power transmission using voltage alone without requiring any electrical current flow through the conductors.
  3. Alternating current voltage levels can be efficiently stepped up and down using transformers to minimize transmission power losses.Answer
  4. D
    Alternating current can be directly stored in standard chemical battery banks at substations without needing rectification.

Answer

Alternating current voltage levels can be efficiently stepped up and down using transformers to minimize transmission power losses.
Alternating current produces a continuously alternating magnetic field that allows transformers to efficiently step up voltage to very high levels for long-distance transmission, which lowers current and minimizes resistive heat losses (I2RI^2R). Transformers can then step the voltage down to standard consumer levels.

Step-by-Step Solution

1
Identify the primary electrical requirement for long-distance power distribution.
Long-distance lines suffer power loss proportional to the square of current (Ploss=I2RP_{\text{loss}} = I^2R). Reducing current by raising voltage reduces energy loss.
Transmission cables have inherent resistance over miles of wire, creating significant power dissipation if current is high.
2
Evaluate the operational principle of transformers with alternating current versus direct current.
Transformers rely on mutual electromagnetic induction, which requires a constantly changing magnetic field generated by alternating current.
Steady direct current does not produce a continuous rate of change in magnetic flux, preventing transformers from stepping direct current voltages up or down.
3
Connect transformer functionality to the preference for alternating current in power distribution grids.
Alternating current can be stepped up to hundreds of kilovolts for efficient transmission and stepped down to safe voltages for end users.
This ease of voltage transformation makes alternating current the standard choice for long-distance power grids.

Key Concept

Transformer compatibility and transmission efficiency differences between alternating current and direct current.
Estimated Time:45s
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Topics

Direct Current (DC) vs. Alternating Current (AC)

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