The quantity calculated by dividing the primary voltage rating by the secondary voltage rating is called the

• A. Turns ratio
• B. Voltage gain
• C. Current ratio
• D. Impedance ratio

Answer: (A)

In a transformer, voltages scale with the number of turns on each winding, so the ratio of the primary voltage to the secondary voltage matches the turns ratio Np/Ns in an ideal transformer. Dividing the primary voltage rating by the secondary voltage rating gives exactly that turns ratio. This is why the turns ratio is the best answer: it directly expresses how many times the primary voltage is compared to the secondary.

Voltage gain is usually defined as Vs/Vp, the inverse of this ratio, so it wouldn’t match the quantity described. The current ratio is the inverse of the turns ratio in an ideal transformer (Ip/Is = Ns/Np). Impedance ratio is the square of the turns ratio (Zp/Zs = (Np/Ns)^2).