靜電學(physic)

The two cases are discussed below:
For paper, when placed near charges (electric field), as paper is insulator, the electric field causes the positive charges of paper to one side of the paper (the opposite side of the paper), and the negative charges moving to the other side. Hence, after the paper is placed near charged metal, it is still neutral. However, the distribution of the charges are uneven. Since like charges repel and opposite charges attract, and since opposite charges are closer to the charged metal, the attraction force is stronger than the repulsive force, causing the paper to stick to the charged metal.

However, as for the aluminium foil, when placed near the charged metal, the charges move to either side of the metal. Yet instantly, the charges redistribute so the the distribution of charges become even. Hence, the charges are evenly distributed and no attraction between the foil and charged metal.

紙屑 = 絕緣體 = 充電後會停留在特定的地方, 即不會亂跑。

鋁箔 = 導電體 = 充電前自由電子不分正負, 充電後會立刻被導致正負分明, 變成中性, 。

金屬棒 = 導電體 = 當有高壓電供應時充電, 只要將電源切斷, 立刻不帶電, 冇嗮吸引力。

It is because aluminium foils are good eelctrical conductors. They will be neutralized instantly when they get in touch with the charged metal rod.