英语翻译In very general terms,an emf is a potential difference,a

英语翻译
In very general terms,an emf is a potential difference,and that is a potential-energy difference per unit charge.A potential-energy difference per unit charge coresponds to work done per unit charge,which is force per unit charge times distance,and that's electric field times distance.The emf exists only as a result of the presence of electric field:(后面是电动势积分环路公式）
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