Transformer Voltage Ratio

Steps:

• Use the transformer equation: Vp/Vs = Np/Ns for ideal (100% efficient) transformer.
• Substitute values: 240/12 = 200/Ns.
• Simplify ratio: 20 = 200/Ns.
• Solve for Ns: Ns = 200/20 = 10 turns.

Why A is correct:

• Turns ratio Ns/Np = Vs/Vp = 12/240 = 1/20, so Ns = 200 × (1/20) = 10, matching step-down for 12V output.

Why the others are wrong:

• B. 14: Wrong ratio; 200/14 ≈ 14.3, not 20.
• C. 4000: Inverts coils, treating as step-up: Ns = 200 × (240/12) = 4000.
• D. 8000: Doubles C, perhaps erroneously multiplying by 40 instead of 20.

Final answer: A