An ideal transformer does not change:

Voltage:
- An ideal transformer is a theoretical device that is used to transfer electrical energy between two circuits through electromagnetic induction.
- It consists of two coils, called the primary and secondary coils, which are wound around a common magnetic core.
- The primary coil is connected to the source of electrical energy, while the secondary coil is connected to the load.
- The primary coil is energized with an alternating current, which creates a changing magnetic field that induces a voltage in the secondary coil.
- The voltage induced in the secondary coil is directly proportional to the number of turns in the coil and the rate of change of the magnetic field.

Current:
- According to Faraday's law of electromagnetic induction, the voltage induced in the secondary coil is given by the equation V = N*dΦ/dt, where V is the induced voltage, N is the number of turns in the coil, Φ is the magnetic flux, and dt is the change in time.
- Since an ideal transformer has a perfectly efficient magnetic core and no losses, the magnetic flux in the primary and secondary coils is the same.
- Therefore, the rate of change of the magnetic flux, dΦ/dt, is also the same in both coils.
- As a result, the voltage induced in the secondary coil is directly proportional to the number of turns in the coil and the rate of change of the magnetic field, and it is equal to the voltage in the primary coil.

Power:
- The power in an electrical circuit is given by the equation P = VI, where P is the power, V is the voltage, and I is the current.
- Since the voltage in the primary and secondary coils of an ideal transformer is the same, the power in the primary coil is equal to the power in the secondary coil.
- Therefore, an ideal transformer does not change the power in the circuit.

Conclusion:
- In summary, an ideal transformer does not change the voltage or power in the circuit.
- However, the current in the primary and secondary coils may be different, depending on the turns ratio of the transformer.
- An ideal transformer is a useful device in many applications, such as voltage conversion, impedance matching, and isolation.