14. 一個半徑2 ?的圓型導體線圈，受到一個方向不變、大小會時變的均勻磁場作用。磁場的方向與線圈截面的方向垂直，線圈感應出5 ?的電動勢。問：磁場大小的時變率？ (A) (B)(C)(D)

9. Choose the correct equation for the standard enthalpy of formation of CO(g), where ΔHf° for CO = –110.5 kJ/mol (gr indicates graphite). (A) 2C(gr) + O2(g) → 2CO(g), ΔH° = –110.5 kJ (B) C(gr) + O(g) → CO(g), ΔH° = –110.5 kJ (C) C(gr) + O2(g) → CO(g), ΔH° = –110.5 kJ (D) C(gr) + CO2(g) → 2CO(g), ΔH° = –110.5 kJ (E) CO(g) → C(gr) + O(g), ΔH° = –110.5 kJ