Physics for IGCSE & O level - Magnets And Currents (Section 9 - No. 1)

In a transformer, the ratio of output voltage to input voltage is equal to the ratio of :

Input current to output current

Number of turns in secondary to primary coil

Number of turns in primary to secondary coil

Input power to output power

This is a core principle of transformer operation, with the voltage ratio matching the turns ratio.