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Lesson: Chapter 19 — Current Electricity

19.1. Static and current electricity 2 of 5

Rubbing and attraction

Static electricity is easy to make and easy to see. The whole demonstration is a comparison: the same object, rubbed and unrubbed.

Try it

  1. Take a drinking straw and rub it well with a piece of cotton cloth.
  2. Bring the rubbed straw close to some very small pieces of paper.
  3. Now bring an unrubbed straw close to the same pieces of paper.

Figure to be added

Figure 19.1 — a drinking straw being rubbed along its length with a piece of cotton cloth.

Observation

The small pieces of paper are attracted to the rubbed straw.

They are not attracted to the unrubbed straw at all.

The same thing with a comb

Take a plastic rod, a pen and a comb, rub each on your hair, and hold it near small pieces of paper or very small pieces of rigifoam. They are pulled towards the rubbed object. Try an unrubbed plastic rod as well, and nothing is attracted.

Figure to be added

Figure 19.2 — very small pieces of rigifoam clinging to a comb that has been charged by rubbing.

What the rubbing gave it

Rubbing gives an object a force that can pull small pieces of paper, dust and similar things towards it — an attractive force. The object gets that force because of the static electric charges that arise on it during the rubbing.

The rubbing is what does it

A straw or a comb attracts small pieces of paper only after it has been rubbed. Leave out the rubbing and it attracts nothing — which is the evidence that the rubbing is what puts the charge there.