Learning objectives By the end of this chapter, you should be able to:
explain the effects of electron addition or removal demonstrate how charges can repel or attract illustrate how charges can be separated by induction
detail the main parts and uses of the gold leaf electroscope
identify how charges spread out on certain-shaped conductors
calculate the forces between charges and the electric field strength present
understand the risks and applications of static electricity.
Electrical charges
The two types of electricity you will study on the Leaving Certificate Physics course are static and current electricity. ‘Static’ means to stay still or unmoving. However, as you will see later in this chapter, static electricity can jump from surface to surface.
Electrical charges come from basic atomic theory. An atom consists of:
• protons, which have a positive charge • neutrons, which have a neutral charge • electrons, which have a negative charge.
NOTE
You will study these in greater detail in Chapters 30 and 31.
A body becomes positively charged when it loses electrons. Conversely, it becomes negatively charged when it gains electrons. Only electrons move.
The size of a charge is based on the number of electrons missing or present. Charge is a scalar quantity and is measured in coulombs (C). One coulomb is equivalent to the charge on 6.25 × 1018 electrons, so that the charge on one electron is 1.6 × 10–19 C.
Opposite charges attract each other and like charges repel each other. This can be easily demonstrated by bringing charged objects close together and observing the attraction or repulsion.
