Examkin

Question

Difficulty: HardFundamentals of Electromagnetism and Induction

A technician connects a primary coil wound around a soft iron core to a constant 12 V12\text{ V} direct current (DC) supply, establishing a steady magnetic field through an adjacent secondary coil. Which of the following modifications will produce a continuous, sustained output voltage across the secondary coil?

  1. A
    Increasing the steady DC supply voltage from 12 V12\text{ V} to 24 V24\text{ V} while holding the current constant
  2. Replacing the DC supply with an alternating current (AC) source to continuously vary the magnetic fluxAnswer
  3. C
    Reversing the DC terminal polarity so that steady electron flow moves in the opposite direction
  4. D
    Doubling the number of turns in the secondary winding while maintaining the steady DC input

Answer

Replacing the DC supply with an alternating current (AC) source to continuously vary the magnetic flux
According to Faraday's law of induction, an electromotive force (EMF) is only induced when there is relative motion or a changing magnetic flux linking the conductor. An alternating current (AC) continuously cycles in amplitude and direction, generating an expanding and collapsing magnetic field that sustains a continuous output voltage in the secondary coil.

Step-by-Step Solution

1
Apply Faraday's Law of Electromagnetic Induction
The induced electromotive force is given by E=−NdΦdt\mathcal{E} = -N \frac{d\Phi}{dt}, where dΦdt\frac{d\Phi}{dt} represents the rate of change of magnetic flux.
Induction strictly depends on a dynamic, changing magnetic field rather than a static magnetic field.
2
Evaluate the magnetic field produced by steady DC
A steady direct current creates a constant magnetic flux (dΦdt=0\frac{d\Phi}{dt} = 0), producing 0 V0\text{ V} across the secondary winding in steady state.
Static direct currents cannot sustain continuous transformer action or mutual induction.
3
Determine the condition for continuous, sustained induction
Supplying alternating current (AC) causes the magnetic flux to expand and collapse continuously, providing a perpetual non-zero dΦdt\frac{d\Phi}{dt}.
Continuous induction requires a continuously oscillating or varying current source.

Key Concept

Electromagnetic Induction and Time-Varying Magnetic Flux
Estimated Time:1m 0s
Rate this question

Topics

Fundamentals of Electromagnetism and Induction

More questions from this topic