Answer: 9 Turns
Explanation: primary turns + secondary turns.
The smallest total number of turns (primary turns plus secondary turns) you will need to build the transformer is 9 turns
Nₛ / Nₚ = Vₛ / Vₚ
Nₛ / Nₚ = 245 / 70
Nₛ / Nₚ = 7 / 2
Thus,
Total turns = Nₚ + Nₛ
Total turns = 2 + 7
Total turns = 9 turns
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