Transformer questions with solutions

Showing 1–10 of 10 questions

• MCQmediumElectromagnetic InductionTransformer

  A transformer supplies 10 kW at 96% efficiency. At this load its copper loss is 250 W. Core loss is constant. If the load current is halved at the same power factor and approximately constant secondary voltage, what is the new efficiency closest to?

  Options

  • Option A

    94.1%

  • Option B

    95.2%

  • Option C

    96.8%

  • Option D

    97.5%

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• MCQmediumElectromagnetic InductionTransformer

  An ideal transformer has Nₚ=1000 and Nₛ=200. A 100 Ω resistor is connected across the secondary. What effective resistance is seen from the primary?

  Options

  • Option A

    4 Ω

  • Option B

    20 Ω

  • Option C

    500 Ω

  • Option D

    2500 Ω

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• Multi-correctmediumElectromagnetic InductionTransformer

  For an ideal step-up transformer operating under load, which statements are correct?

  Select all that apply

  • Option A

    Vₛ>Vₚ.

  • Option B

    Iₛ<Iₚ.

  • Option C

    Input power equals output power.

  • Option D

    It can increase both voltage and current while also producing more output power than input power.

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• Multi-correctmediumElectromagnetic InductionTransformer

  An ideal transformer is connected to a fixed primary RMS voltage. The secondary load resistance is reduced to one-fourth of its original value. Which statements are correct?

  Select all that apply

  • Option A

    Secondary current becomes four times.

  • Option B

    Primary current becomes four times.

  • Option C

    Reflected primary resistance becomes one-fourth.

  • Option D

    Input power becomes sixteen times.

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• MCQmediumElectromagnetic InductionTransformer

  A load resistance R is connected across the secondary of an ideal transformer. What resistance is reflected to the primary?

  Options

  • Option A

    (Nₛ/Nₚ)²R

  • Option B

    (Nₚ/Nₛ)²R

  • Option C

    (Nₚ/Nₛ)R

  • Option D

    R

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• Multi-correctmediumElectromagnetic InductionTransformer

  A transformer has constant iron loss 400 W and full-load copper loss 900 W. Secondary voltage is approximately constant with load. Which statements are correct?

  Select all that apply

  • Option A

    Maximum efficiency occurs at two-thirds of full-load current.

  • Option B

    At maximum efficiency copper loss is 400 W.

  • Option C

    At maximum efficiency total internal loss is 800 W.

  • Option D

    Maximum efficiency occurs when copper loss equals iron loss.

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• NumericmediumElectromagnetic InductionTransformer

  An ideal transformer has 500 primary turns and 100 secondary turns. A 20 Ω resistor is connected across the secondary and the primary is supplied with 200 V RMS. Determine the primary RMS current, in ampere.

  Your answer

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• Multi-correctmediumElectromagnetic InductionTransformer

  Which effects reduce the efficiency of a practical transformer?

  Select all that apply

  • Option A

    Copper loss in windings.

  • Option B

    Eddy-current loss.

  • Option C

    Hysteresis loss.

  • Option D

    Flux leakage.

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• MCQmediumElectromagnetic InductionTransformer

  A transformer designed for a fixed RMS voltage and frequency is supplied with the same RMS voltage at a substantially lower frequency. What happens to the maximum core flux, neglecting saturation?

  Options

  • Option A

    It decreases.

  • Option B

    It increases.

  • Option C

    It is unchanged.

  • Option D

    It becomes zero.

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• A/RmediumElectromagnetic InductionTransformer

  Consider a conventional transformer connected to a DC source.

  Assertion

  A conventional transformer cannot continuously step up a constant DC voltage merely by using more secondary turns.

  Reason

  A steady primary current produces no continuously changing magnetic flux and hence no sustained secondary EMF.

  Options

  • Option A

    Both A and R are true and R is the correct explanation of A.

  • Option B

    Both A and R are true but R is not the correct explanation of A.

  • Option C

    A is true but R is false.

  • Option D

    A is false but R is true.

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