Discharging Insulator 40

You questions are interesting. I did not think about these before.

As you said, it is an insulator. So earthing cannot discharge it. I suppose it is like rubbing a plastic ruler over hair to produce a charge on the plastic ruler. If you put one end of the plastic ruler onto the ground, you cannot discharge the whole ruler because plastic is an insulator, which cannot conduct current efficiently. You can discharge a charged metal object by earthing. But you cannot discharge a charged insulator by earthing.

The only way I can think of discharging a charged insulator is to pour water onto the charged insulator. Water covering the whole surface of the insulator will discharge it.

2011-01-21 17:48:59 補充：
Dear Tin Tung,

I agree with you. The so-called insulators can discharge by earthing if you allow long enough time.

But in reality, when I am standing on the ground without shoes and holding a charged plastic ruler with my bare hand, the charge on the plastic ruler can last quite long.

2011-01-21 17:49:29 補充：
.......

This indicates that earthing is not an effective way to discharge a charged insulator. And that is why yuet asked the questions.

Why not ?
If you earth a charged insulator, it will be at earth potential. All the charges on it will be gone because of the potential difference set up between the insulator and earth.

2011-01-21 09:05:54 補充：
I think it is incorrect to say that, as in the post below, an insulator cannot be discharged by earthing, unless the insulator is an absolutely perfect one. But such perfect insulator is not in existence in the world...(cont'd)

2011-01-21 09:06:32 補充：
...Any potential difference between the an object (insulator) and earth will drive a current. Potential differences that usually dealt with in electrostatics are quite high (as every physics students must know that electrostatics deals with small charge and high potential)....(cont'd)

2011-01-21 09:07:00 補充：
...Practical insulators does allow minute current to flow. The difference between an insulator and a conductor (which is, in fact, a poor insulator) is that the discharge time for the former is much longer than that for the latter.

2011-01-21 13:49:29 補充：
...The term that is used for describing how insulators conduct is "leakage" (or "leakage current"). Insulator does leak, especially under high potential condition.