Like mass and length, electric charge is a fundamental property of all matter. Matter is made up of atoms and molecules; atoms contain electrons (negative charge), protons (positive charge) and neutrons (no charge). An electric current consists of moving electric charges. This chapter covers electric charge, field and potential, electric current, e.m.f, potential difference, resistance, circuit diagrams, the effects of current, dc and ac, and safety with electricity.
1. Electric Charge
Atoms and Ions
- The nucleus holds positively charged protons and chargeless neutrons; negatively charged electrons orbit the nucleus.
- Usually an atom has as many electrons as protons, so atoms are neutral.
- If an electron is removed, the atom becomes positively charged – a positive ion.
- If an electron is added in excess, the atom becomes negatively charged – a negative ion.