In an ideal transformer, the turns ratio is $\frac{N_p}{N_s}=\frac{1}{2}$. The ratio V_S : V_P is equal to (the symbols carry their usual meaning) :

The correct option/answer is 2:1.

To find the ratio of the secondary voltage to the primary voltage, we use the fundamental principle of an ideal transformer. For an ideal transformer, the voltage across the winding is directly proportional to the number of turns in that winding.

This relationship is expressed by the transformer equation:
$\frac{V_s}{V_p}=\frac{N_s}{N_p}$
where:
- _Vp and _Vs represent the primary and secondary voltages, respectively.
- _Np and _Ns represent the number of turns in the primary and secondary coils, respectively.

We are given the turns ratio as:
$\frac{N_p}{N_s}=\frac{1}{2}$

Taking the reciprocal of the given turns ratio, we obtain the ratio of the secondary turns to the primary turns:
$\frac{N_s}{N_p}=\frac{2}{1}$

Substituting this value back into the voltage ratio relation gives:
$\frac{V_s}{V_p}=\frac{2}{1}$

Therefore, the ratio V_s : V_p is equal to 2:1.