Electric Charge

Only two types: positive and negative

Same charges (++ or −−) repel each other, opposite charges (+−) attract each other.

Conductor

Materials where electric charges are free to move around through the material.

EX: metals

Insulator

Materials where excess charges placed in/on the material remains fixed.

EX: plastic, glass, ceramics

Semiconductors

Materials that act like conductors and insulators.

Electric Charge and the Structure of Matter

Subatomic particles responsible for electric charge: electrons (−) and protons (+).

Each element has fixed number of protons, but differing number of electrons results in ions:

• default neutrally charged atom has an equal number of protons and electrons (see #2 below)
• cation (positive ion) — loss of electrons
• anion (negative ion) — gain of electrons

Conservation of Electric Charge

1. The algebraic sum of all the electric charges (net charge) in any closed system is constant.
2. The magnitude of charge of an electron is equal to the magnitude of charge of a proton and is the natural unit of charge.

Rubbing an initially uncharged glass rod with an initially uncharged piece of silk fabric will result in a positively charged rod and a negatively charged piece of silk of the same magnitude. The charges are merely transferred from one body to the other.