Effect of speed on induced EMF: In a basic direct-current (DC) generator, if the loop suddenly rotates faster, what happens to the induced voltage?

Difficulty: Easy

Correct Answer: increases

Explanation:


Introduction / Context:
In electromechanical energy conversion, the induced EMF in a rotating conductor cutting magnetic flux depends on rotational speed. This principle governs generator output behavior with changing speed at constant field strength.


Given Data / Assumptions:

  • Same magnetic flux per pole (field strength unchanged).
  • Only the mechanical speed is increased.
  • Basic DC generator with commutation maintaining output polarity per half-turn in the usual manner.


Concept / Approach:

The magnitude of induced EMF in a generator is proportional to the rate of flux cutting, which is proportional to angular velocity omega. In simplified form, E ∝ phi * omega. With phi constant, increasing speed raises E proportionally.


Step-by-Step Solution:

Assume field flux phi is constant.Increase speed: omega → k * omega, k > 1.Then E_new = k * E_old (direct proportionality).


Verification / Alternative check:

Practical machines show higher terminal voltage at higher speed if field and load remain unchanged (until regulation or saturation effects intervene), consistent with the theoretical relation.


Why Other Options Are Wrong:

'Remains unchanged' contradicts E ∝ speed. 'Reverses polarity' would require reversing rotation direction or field polarity, not merely increasing speed. 'Decreases' is opposite to the physical relationship. 'Drops to zero' has no basis unless the field collapses.


Common Pitfalls:

Confusing AC generator phase effects with DC commutation, or assuming internal regulation keeps voltage constant, which is not implied here.


Final Answer:

increases

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