關於d.c.同a.c.

1. Earthing keeps the potential of the wire at zero volt. Apart from safety reason, this also helps to maximize the voltage supplied by the live wire.

2. Not necessariyl. We can only know for sure that there is a volatge drop arcoss the light bulb. The exact potential is not known unless one end of the light bulb is earthed, i.e. a reference potential is known.

3. There will then be no voltage supplied, because there is no potential difference between the "Live" wire and the "Neutral" wire.

4. An applicance has resistance. There is a potential difference between the end of the applicance that is connected to the "Live" wire and the other end of the appliance connected to the "Neutral" wire. It is because of such potential difference that drives current to flow through the appliance.

5. The "Earth" is always kept at earth (i.e. zero) potential and is connected to the casing of the appliance. When the "Live" wire, under an accidental situation, touches the casing of the appliance. Current would pass through the casing to earth instead of passing through the appliance. Such large current breaks the fuse before there is any effect on the potential of the "Live" wire.

The explanation given by your is right.


2011-10-20 19:56:59 補充：
6. Please refer to answer given in (4). The resistance of the appliance helps to maintain a potential difference between the"Live" and "Neutral" wires.

1. netural唔係earth，另有earth線
2. 量度電壓要有一個參考點，喺咪0v要先知參考點電壓
3. live，netural同earth線係三條獨立線，唔明你點解要earthed，你係邊度學返嚟
4. 你係咁重複要earth，唔明你講乜，earth係一條線，係名詞，唔係動詞
5. earth係保險線，通常接上漏電保護掣，當電器有問題或短路，電流流經金屬外殼會有觸電危險，當外殼接上earth時，漏電電流會流向並觸發保護掣，將live同netural截斷
6. 保險絲同漏保護掣同樣用途，但作用唔同，電器漏電但可能仍可工作而人不為意，而保險絲則防止過大電流，通常都係故障或短路，過大電流會導致電線過熱冒火燒毀電器，保險絲作用係電流大過某額定值就會燒斷，將live線截斷保障生命財產