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When material A is rubbed against material B, A acquires a positive charge and B a negative charge. When the same material A is rubbed against material C, A acquires a negative charge. If now an object of material B is rubbed against an object of material C, what is the result?

1. B becomes positive and C becomes positive.
2. B becomes positive and C becomes negative.
3. B becomes negative and C becomes positive.
4. B becomes negative and C becomes negative.

Correct answer: B becomes negative and C becomes positive.

Solution

A loses electrons to B (A becomes +, so A is more positive-tending than B). A gains electrons from C (A becomes -, so C is more positive-tending than A). The triboelectric ranking (most positive-tending first) is therefore C > A > B. When B and C are rubbed, the more positive-tending one (C) becomes positive and B becomes negative.

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