Examkin

Question

Difficulty: MediumElectromagnetism and Induction

An electrical technician connects a 12 V12\text{ V} DC battery across the primary winding of an iron-core transformer through a switch. After the switch is closed and a steady current is established in the primary winding, what voltage behavior is observed across the secondary winding?

  1. A
    A continuous 12 V12\text{ V} DC output is maintained as long as primary current flows.
  2. B
    A continuous alternating voltage is generated across the secondary terminals.
  3. A brief voltage pulse occurs when the switch closes, followed by zero output while current remains steady.Answer
  4. D
    A constant electrostatic charge accumulates in the core without producing any transient voltage.

Answer

A brief voltage pulse occurs when the switch closes, followed by zero output while current remains steady.
According to Faraday's Law of Electromagnetic Induction, an electromotive force (voltage) is induced in a secondary winding only when there is a changing magnetic flux (e=−NΔΦΔte = -N \frac{\Delta \Phi}{\Delta t}). When the switch is initially closed, the current rises from zero to its maximum level, generating an expanding magnetic field that induces a brief voltage pulse. Once the DC current reaches a steady state, the magnetic field stops changing (ΔΦΔt=0\frac{\Delta \Phi}{\Delta t} = 0), causing the induced secondary voltage to drop immediately to zero.

Step-by-Step Solution

1
Analyze the conditions required for electromagnetic induction according to Faraday's Law.
Induced voltage is directly proportional to the rate of change of magnetic flux (e=−NΔΦΔte = -N \frac{\Delta \Phi}{\Delta t}).
A magnetic field must be expanding, collapsing, or moving relative to a conductor to induce an electromotive force (EMF).
2
Determine the magnetic flux behavior during switch closure versus steady DC state.
During switch closure, current rises from 0 A0\text{ A} to steady state, creating a rapidly expanding magnetic field (brief voltage pulse). Once steady state is reached, current is constant, making ΔΦΔt=0\frac{\Delta \Phi}{\Delta t} = 0, resulting in zero induced secondary voltage.
Steady direct current produces a stationary, unchanging magnetic field that cannot induce voltage in a stationary secondary coil.

Key Concept

Faraday's Law of Electromagnetic Induction and Transformer Operation
Estimated Time:1m 0s
Rate this question

Topics

Electromagnetism and Induction

More questions from this topic