Transformer
V_s/V_p = N_s/N_p. Step-up vs step-down with animated flux in core.
Key Notes
A transformer is two coils (primary, secondary) magnetically coupled — usually via a laminated iron core to maximise flux linkage.
Ideal-transformer relation: V_s/V_p = N_s/N_p (turns ratio).
If N_s > N_p: step-up transformer (V_s > V_p but I_s < I_p). If N_s < N_p: step-down.
For an ideal (lossless) transformer: V_p·I_p = V_s·I_s (power conservation).
Transformers ONLY work with AC — they need a changing Φ. DC produces no induction.
Real transformers have losses: copper (I²R in windings), iron (eddy + hysteresis in core), flux leakage. Efficiency typically 95-99%.
Power transmission grid uses high-voltage AC (220-765 kV) precisely so transformers can step it up at the source and step it down at the consumer end — minimising I²R losses in transmission lines.
Formulas
Turns / voltage ratio
Same flux per turn ⇒ EMF scales with turns.
Current ratio (ideal)
From power conservation V_p I_p = V_s I_s.
Reflected impedance
Load resistance looks DIFFERENT from the primary side.
Efficiency
Modern power transformers reach 99%.
Important Points
Transformers conserve POWER (in the ideal case) — they trade voltage for current.
Step-up at the power plant raises V (drops I) → tiny I²R losses in transmission lines. Step-down at the city.
Laminated cores reduce eddy-current losses. Silicon-iron alloy reduces hysteresis losses.
Flyback transformers operate at high frequencies (10-100 kHz) to allow smaller cores — laptop chargers, switching power supplies.
DC cannot drive transformers — it produces dΦ/dt = 0 ⇒ no induced EMF. (Pulsed DC works, but it's effectively AC.)
Transformer impedance matching: an audio amplifier output transformer matches the high-impedance tube/transistor output to a low-impedance speaker.
Transformer notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.