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⚛️ Physics  ·  Alternating Current  ·  NEET & JEE

In a step-up transformer, if the primary has N<sub>1</sub> turns and secondary has N<sub>2</sub> turns (N<sub>2</sub> > N<sub>1</sub>), then:

Answer: V 2 > V 1 and I 2 1.

  • A V<sub>2</sub> > V<sub>1</sub> and I<sub>2</sub> < I<sub>1</sub>
  • B V<sub>2</sub> < V<sub>1</sub> and I<sub>2</sub> > I<sub>1</sub>
  • C V<sub>2</sub> = V<sub>1</sub>
  • D V<sub>2</sub> > V<sub>1</sub> and I<sub>2</sub> > I<sub>1</sub>

Correct answer: A. V<sub>2</sub> > V<sub>1</sub> and I<sub>2</sub> < I<sub>1</sub>

Explanation: V<sub>2</sub>/V<sub>1</sub> = N<sub>2</sub>/N<sub>1</sub>. For N<sub>2</sub> > N<sub>1</sub>, voltage increases. By energy conservation (ideal transformer): V<sub>1</sub> I<sub>1</sub> = V<sub>2</sub> I<sub>2</sub>, so current decreases.

V and I Phase Relationships in AC CircuitsPure Inductor: I lags V by 90°VIPure Capacitor: I leads V by 90°VIMemory aid "ELI the ICE man": in an inductor (L) E(V) leads I; in a capacitor (C) I leads E(V)For a pure resistor, V and I stay perfectly in phase (no lag or lead at all)

In a pure inductor the current lags the voltage by 90° (energy is briefly stored in the magnetic field before current responds); in a pure capacitor the current leads the voltage by 90° (current must flow to build up charge before voltage rises) - the mnemonic "ELI the ICE man" keeps these straight.

Concept context

AC circuits, impedance, LCR series circuit, resonance, transformers, and power factor.

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