The electroscope: a measuring instrument built by yourself

Evaluation:

Sometimes it is difficult to observe the experiment exactly. You can watch the video again before thinking about the questions.

The closer the rod comes to the aluminium foil, the wider the cut-off pieces strive apart. Even without touching the foil, the strips move. If the pastic rod is removed again, it will lose its influence on the foil and so it will sink down again.

How can the impact of the plastic on the aluminium foil be explained?

a) The nearby charge of the plastic shifts the charge in the aluminium foil. Consequently, identical charges gather down below and repel each other.

b) The plastic has been charged by rubbing. But its force is only sufficient to attract one of the two foils. So one foil is moving away from the other.

c) The plastic has been charged strongly by rubbing. This charge is now transferred to the aluminium foil. Due to the fact that now both of them are charged, they attract each other and the sections of the foil move upwards.