phys神手請進~~~~

兩幅都岩,左邊o個幅比較普遍
你不能得知電線的確實電勢,除非題目有寫明,
但你可以知道兩邊電線的電勢差(potential difference)係6v,
所以你可以假設負極端既電勢係零,而正極端係6v,方便計算.
概念同你應用PE=mgh好相似,
h一般會設地面係0,
但唔一定,最要既係h1&h2既差值.

In fact, both diagrams are right.

You could not determine exactly the potential at any point in the circuit if you do not make a reference point in the circuit for potential calaculation. Generally, the negative pole of a battery is taken as a reference point and assume that it is at zero potential. Under this situation, the +ve pole of the battery in your example is clearly at +6 v.

因為電流冇得負lo!