Ideal transformer voltage and current ratios
Turns change voltage and current while conserving ideal power.
Key knowledge
For ideal coupled windings linking the same time-varying flux, voltage amplitudes satisfy N_pV_s=N_sV_p. With negligible magnetizing current and losses, corresponding load-current magnitudes satisfy N_sI_s=N_pI_p. Step-up voltage therefore accompanies reduced current at the same ideal transferred power; a transformer does not maintain this action from constant DC flux.
Values and equations
N_pV_s=N_sV_p; N_sI_s=N_pI_p
- V_s,V_p
- Correspondingly oriented secondary/primary sinusoidal voltage magnitudes V
- I_s,I_p
- Secondary load/primary input current magnitudes in the ideal limit A
- N_s,N_p
- Positive turn counts 1
Conditions and scope
- Shared flux, fixed integer positive turns, stated terminal polarity, negligible leakage/resistance/core loss and appropriate time-varying steady operation.
- Finite magnetizing current, saturation, parasitic capacitance and frequency response limit a real transformer. Power is the average of instantaneous voltage×current; rms magnitudes alone need a matching power-factor interpretation.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read §15.6 common-flux voltage derivation15.20–15.21, the unnumbered ideal transferred-power identity and current relation15.22. Cross-multiplied turn relations are disclosed algebraically equivalent forms that remain defined at zero voltage/current. Explicitly scope magnetizing current and sinusoidal magnitude convention; exclude unqualified rms-product power claims for arbitrary loads.
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Entry details
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- foundation-physics-ideal-transformer
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions