. If we have a higher resistance, then we would have a greater power loss. So ideally, you'd want a low resistance for a low power loss.

If the secondary coil has a lower voltage output, then it will have a higher current flowing through it. From the formula, you can see that a high current will contribute to a greater power loss. Because of this, we need to decrease resistance to decrease power loss. As kawaiipotato has said, this is achieved by using a thicker wire. This is because resistance is inversely proportional to the cross-sectional area of the conductor the current is flowing through (greater cross-sectional area=lower resistance). So there needs to be a thicker wire in the secondary coil of a step-down transformer as it decreases resistance and thus power loss, allowing for a more energy efficient transfer of electricity.