정답: 1번

아크의 출력 전력은 \( P_{\text{arc}} = V_{\text{arc}} \times I_{\text{arc}} = 25 \, \text{V} \times 300 \, \text{A} = 7500 \, \text{W} \).

총 입력 전력은 \( P_{\text{input}} = P_{\text{arc}} + \text{내부손실} = 7500 \, \text{W} + 4000 \, \text{W} = 11500 \, \text{W} \).

효율은 \( \eta = \left( \frac{P_{\text{arc}}}{P_{\text{input}}} \right) \times 100 = \left( \frac{7500}{11500} \right) \times 100 \approx 65.2\% \).