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Why have a transformer? Why not just connect the secondary to the primary directly? The voltage and current can be adjusted between the primary and secondary by changing the number of loops in each. If the primary has $$100$$ loops and the secondary $$10$$ loops the voltage in the secondary will be $$1/10$$ of the voltage in the primary but the current in the secondary will be $$10$$ times that of the primary. The voltage ratio between primary and secondary is proportional to the ratio in the number of turns of wire in each. This makes it easy to step up voltage (while stepping down current) or step down voltage (while stepping up current).