What does a transformer do and how is the turns ratio related to voltage?

• A. Steps up DC voltage
• B. Blocks DC
• C. Transfers AC power; Vp/Vs = Np/Ns
• D. Converts AC to DC

Answer: (C)

A transformer transfers electrical energy between two circuits using mutual induction, so it moves power from the primary winding to the secondary without a direct electrical connection. It only works with alternating current because the changing magnetic flux in the core is what induces voltage in the secondary; a steady DC would just saturate the core and stop producing a useful output. The voltages on the windings are set by the turns ratio: Vp/Vs = Np/Ns, which means the secondary voltage is Vs = Vp × (Ns/Np). This is how stepping up or stepping down works—more turns on the secondary raise the voltage, fewer turns lower it. In an ideal transformer, power in roughly equals power out, so the currents adjust inversely with the turns.