Question

When a glass rod is rubbed with silk, it becomes positive and the silk becomes negative, yet both attract dust. Is it possible the dust has a third type of charge that is attracted to both positive and negative? Explain. Which model: 2 types or 3 types of charge would be a simpler model?

Answer 1

There is no third charge.

In case of positively charged glass rod, it induces negative charge in the neutral dust particles and the face of particle nearer to rod becomes negatively charged while the opposite face acquires equal positive charge ensuring the neutrality of dust particles while still being attracted to the rod.

In case of negatively  charged silk, it induces positive charge in the neutral dust particles and the face of particle nearer to silk becomes positively charged while the opposite face acquires equal negative charge ensuring the neutrality of dust particles while still being attracted to the rod.

This explains how both positive charged rod and negatively charged silk attract dust.

Hence no third charge model is needed.

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