Electric Charge (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

• There are two types of electric charge: positive and negative
• Inside an atom, there are
  • negatively charged electrons
  • positively charged protons
  • neutral (no charge) neutrons

• Atoms contain equal numbers of protons and electrons as they have equal and opposite charges
• These charges cancel out so the overall charge of an atom is zero

Structure of an atom

The number of negative electrons in an atom balances the number of positive protons

Attraction and repulsion

• When two charges are close together, they exert a force on each other, this could be:
  • Attractive (the objects get closer together)
  • Repulsive (the objects move further apart)

Electric forces between charges

Opposite charges attract, like charges repel

• Whether two objects attract or repel depends on their charge
  • If the charges are the opposite, they will attract
  • If the charges are the same, they will repel

Attraction or repulsion summary table

Charge of object 1	Charge of object 2	Attract or repel?
positive	positive	repel
positive	negative	attract
negative	positive	attract
negative	negative	repel

 

• The table shows that:
  • Positive charges repel other positive charges and attract negative charges
  • Negative charges repel other negative charges and attract positive charges

Extended tier only

• Electric charge is measured in units called coulombs (C)