Charges can be ‘transferred’ through electrons or ions in order to reach a neutral state, where possible. The same basic law that opposites attract and like charges repel is used.
Charge transfer can be categorized into 4 types:
- Conduction
- Polarization & Induction
- Friction (Also called triboelectric charge)
| Type | Material |
|---|---|
| Conduction | Conductors & Insulators |
| Polarisation | Conductors & Insulators |
| Friction | Insulators only |
| Induction | Conductors only |
Conduction
When a charged body comes into direct contact with another body, the electrons in it quickly spread, based on the polarity.
- If the charged object is negatively charged (i.e. has excessive electrons), the electrons quickly get attracted to by the nuclei of the other body, moving over and thus spreading charge.
- Alternatively, if the charged object is positively charged (i.e. lack of electrons), the electrons from the neutral body get pulled by the nuclei of the charged body, spreading charge
In a conductor, the charge easily spreads throughout the second body, whereas in an insulator, the charge merely ‘sticks’ to the surface on the point of contact:
Friction - Triboelectric Charge
Another key property of materials is electron affinity. In simple terms, electron affinity is how likely a material is to pull electrons from it’s surroundings, even when in neutral. In a triboelectric table, we can see that metals stay in the central, as they are mostly stable, while non-metals tend to both ends. The easiest way to interpret a triboelectric series is that if material A is below material B, then B donates electrons to A during friction. As such, friction is usually associated with insulators
This means rubbing a glass rod, with, for example, a piece of wool, will result in the wool ‘stealing’ the electrons from the glass, as it is lower on the series. Thus, the glass rod will become positively charged, while the wool will become negatively charged. However, the net charge is still the same:
Polarization & Induction
This type of charge transfer affects both conductors and insulators. Because of the free moving electrons in the material, a charged object can still influence a conductor without touching it. IN insulators, the electrons can face the electric field without actually moving, achieving a similar effect. The electrostatic force, is, in some cases, strong enough to cause an imbalance of electrons in the material, creating a dipole:
Induction is a method of making an object charged without touching it, using the earth to ground the object. It only works for conductors, because insulators cannot readily be grounded.