What does a step-up transformer do?

A step-up transformer is designed specifically to increase the voltage of an electrical signal while decreasing the current proportionally. This process occurs due to the way the transformer is constructed, utilizing coils of wire wound around a magnetic core.

When an alternating current passes through the primary winding (input side) of the transformer, it generates a magnetic field that induces a voltage in the secondary winding (output side). In a step-up transformer, the secondary winding has more turns of wire than the primary winding. According to Faraday's law of electromagnetic induction, the voltage increase is directly related to the ratio of the number of turns in the secondary winding compared to the primary winding.

For example, if the primary winding has 50 turns and the secondary has 100 turns, the voltage will be doubled (assuming ideal conditions without losses). This increased voltage allows for the efficient transmission of power over long distances, as higher voltage levels reduce current flow and consequently decrease line losses due to resistance.

The other options relate to actions that are opposite to the function of a step-up transformer; a step-up transformer does not decrease voltage or increase current, but rather precisely increases voltage while causing a decrease in current.