～～有關電動學～～

electromotive force (e.m.f.)乃是

當1 C charges流入電源(e.g. cell, battery)時, 得到幾多electrical energy (change from chemical energy from cell).

e.m.f. = E / Q

potential difference (p.d.)乃是

當1 C charges流入load(e.g. resistor, light bulb...)時, 提供幾多electrical energy給它們 (change to internal of the resistor).

p.d. = E / Q

因公式是一樣, 同時也是能量轉換, 故有時以它們同以voltage稱呼.

主要不同是e.m.f.是charges得到能量, p.d.是charges消耗能量.