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⚛️ Physics  ·  Alternating Current  ·  NEET & JEE

A step-down transformer (20:1 ratio) is connected to 2200 V AC. The secondary is connected to a 44 W bulb. What is the secondary current and primary current?

Answer: I2 = 0.4 A, I1 = 0.02 A.

  • A I2 = 0.4 A, I1 = 0.02 A
  • B I2 = 2 A, I1 = 0.1 A
  • C I2 = 0.04 A, I1 = 2 A
  • D I2 = 44 A, I1 = 2.2 A

Correct answer: A. I2 = 0.4 A, I1 = 0.02 A

Explanation: V2 = V1/20 = 2200/20 = 110 V. I2 = P/V2 = 44/110 = 0.4 A. By energy conservation: I1 = I2/20 = 0.4/20 = 0.02 A.

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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