The voltage ratio in a transformer is determined by the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. This is based on the principle of electromagnetic induction.

  In a transformer, an alternating current flowing through the primary winding creates a changing magnetic field. This changing magnetic field induces a voltage in the secondary winding. The magnitude of the induced voltage is directly proportional to the rate of change in the magnetic field, which is in turn proportional to the number of turns in the winding.

  According to Faraday's law of electromagnetic induction, the induced voltage (Vs) in the secondary winding is given by the equation Vs = Ns * dϕ/dt, where Ns is the number of turns in the secondary winding and dϕ/dt is the rate of change of magnetic flux.

  Similarly, in the primary winding, the applied voltage (Vp) is related to the rate of change of magnetic flux, given by Vp = Np * dϕ/dt, where Np is the number of turns in the primary winding.

  By comparing the equations, we can see that the voltage ratio (Vp/Vs) is equal to the turns ratio (Np/Ns) because the rate of change of magnetic flux is the same for both windings. Therefore, the voltage ratio in a transformer is solely determined by the ratio of the number of turns in the primary and secondary windings.

  It is important to note that transformer operation is based on the principles of ideal transformers. In practical transformers, there are losses and other factors that can slightly affect the voltage ratio, but the turns ratio remains the primary determinant.