Transformers — Flashcards & Quiz

Q1: How does a transformer work and what is the transformer equation?

A transformer transfers electrical energy between circuits using electromagnetic induction. AC in the primary coil creates a changing magnetic flux in an iron core, which induces an EMF in the secondary coil. Transformer equation: V_p/V_s = N_p/N_s = I_s/I_p. Step-up: N_s > N_p. Step-down: N_s < N_p.

Q2: Why do transformers only work with AC and not DC?

Transformers require a CHANGING magnetic flux to induce an EMF in the secondary coil (Faraday's law). AC continuously changes direction, creating a continuously changing flux. DC produces a constant flux — no change means no induced EMF (except briefly when DC is first switched on or off).

Q1: A transformer can work with both AC and DC input.

Answer: FALSE

Transformers require changing flux (Faraday's law). AC provides continuously changing current/flux. DC produces constant flux — no change means no induced EMF in the secondary. Transformers only work with AC.

Q2: A step-up transformer increases voltage and decreases current.

Answer: TRUE

V_s/V_p = N_s/N_p. A step-up has more secondary turns, so V_s > V_p. By conservation of energy (P = VI): if V increases, I must decrease proportionally. V_pI_p = V_sI_s.

Q3: An ideal transformer has 100% efficiency with no energy losses.

Answer: TRUE

An ideal transformer transfers all energy from primary to secondary: P_p = P_s, so V_pI_p = V_sI_s. Real transformers have losses from resistance, eddy currents, hysteresis, and flux leakage, achieving about 95-99% efficiency.