An ideal transformer sets voltage by the turn ratio and trades current the opposite way so power is conserved across the windings. With 3 primary and 6 secondary turns the 6 V doubles to 12 V while current halves from 2 A to 1 A, keeping 12 W on both sides exactly for the ideal lossless, perfectly coupled model; real transformers add core saturation, leakage flux, winding resistance, frequency dependence, heating, load regulation, parasitics, and measurement uncertainty.
An ideal transformer trades voltage and current while preserving power. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
An ideal transformer follows the turn ratio
Primary turns 3 and secondary turns 6 double the voltage from 6 to 12 volts.
12/6=6/3
Current trades so ideal power stays equal
Primary current 2 amperes and secondary current 1 ampere both give power 12 watts.