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Alternating Current — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsAlternating Current1 Mark
Question
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: Step-down transformer increases the current.
Reason: Transformer obeys the law of conservation of energy.
✓

Answer

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

Explanation:

If there is no loss of energy in transformer, then instantaneous output power is equal to instantaneous input power. From this we get $\frac{\text{e}_\text{s}}{\text{e}_\text{p}}=\frac{\text{I}_\text{p}}{\text{I}_\text{s}}.$

So in step up transformer voltage increases by decreasing the current. Similarly, step-down transformer decreases the voltage by increasing current. Therefore transformer simply transforms the voltage and current, obeying the law of conservation of energy.

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