What is the Turns ratio for 19900 (primary) and 120/240 (secondary)?

• A. 82.9:1
• B. 1:82.9
• C. 19900:120
• D. 19900:240

Answer: (A)

Turns ratio is the relationship between the primary turns and the secondary turns in an ideal transformer, written as Np:Ns. The primary winding has 19,900 turns. The secondary is described as 120/240 with a center tap, so the full secondary winding (which corresponds to 240 V) has twice the turns of each half. Therefore the secondary turn count to use for the ratio is the full 240 V winding. The turns ratio is Np:Ns = 19,900:240, which simplifies to about 82.9:1 (19,900 ÷ 240 ≈ 82.9167). So the primary has about 82.9 times more turns than the full secondary. Using the 120 V half would give 19,900:120 ≈ 166:1, which isn’t the listed option.