The correct answer is option 3, which states that a transformer can increase voltage and decrease voltage.

A transformer is an electrical device that is used to transfer electrical energy between two or more circuits through electromagnetic induction. It consists of two or more coils of wire called windings, which are typically wound around a soft iron core.

The primary winding is connected to the power source and the secondary winding is connected to the load. When an alternating current flows through the primary winding, it creates a changing magnetic field in the core, which induces a voltage in the secondary winding.

The primary function of a transformer is to change the voltage level of an AC power supply. If the number of turns in the secondary winding is greater than the number of turns in the primary winding, the transformer is called a step-up transformer and it increases the voltage. If the number of turns in the secondary winding is less than the number of turns in the primary winding, the transformer is called a step-down transformer and it decreases the voltage.

Therefore, a transformer can both increase and decrease the voltage depending on the ratio of turns in the windings. The options 1 (increase power) and 4 (measure current and voltage) are incorrect as transformers do not increase power or have the capability to measure current