Conservation of energy in transformers How does energy remain conserved in a transformer if emf is increasing, or decreasing?
Does the current decreases to accomodate?
Does Ohm's law still hold here? Although we know, Ohm's law is not universal.
 A: Yes you're right. Wikipedia calls this the transformer equation:
$$\frac{V_P}{V_S} = \frac{I_S}{I_P}=\frac{N_\text{P}}{N_\text{S}}=\sqrt{\frac{L_P}{L_S}}$$
$P$ and $S$ denote primary and secondary, respectively. $V,I,N$ and $L$ are emf, current, winding number and inductance. Keeping this ratio constant assures that the power $P=V_SI_S=V_PI_P$ is the same on either side.
A: If you're concerned about Ohm's law, you might be getting a little muddled in your thoughts (don't worry, I only know this because I've had my turn at being muddled before on this point!)
Ohm's law doesn't describe a transformer: Ohm's law may apply to whatever load you connect to the transformer; if so, then Ohm's law combines with the transformer law $V_P\, I_P = V_S\, I_S$ to yield the concept of reflected impedance (as I talk about in the linked answer): a load with impedance $\mathcal{Z}$ connected across the transformer's secondary appears as the load $\left(\frac{N_S}{N_P}\right)^2\,\mathcal{Z}$ at the primary. This generalises to:
$$Z_P \approx \left(Z_{T1}^{-1}+\left(Z_{T2}+\left(\frac{N_S}{N_P}\right)^2\,\mathcal{Z}\right)^{-1}\right)^{-1}$$
in a real transformer, where $Z_{T1}$ and $Z_{T2}$ model the transformer's own ohmic losses and energy storage capacity.
The transformer equation itself can be thought of as either:


*

*A statement of conservation of energy; OR

*A statement that the same flux links the primary and secondary and the consequences of applying (a) Ampère's law to a flux loop threading both primary and secondary to get the current ratio from and (b) Faraday's law to flux time variation, to get the voltage ratio.

