Electric Charge
- Charge is measured in coulombs (C). One coulomb is defined as:
The charge carried by an electric current of one ampere in one second
- Charge is a scalar quantity
- Electrons have a negative charge
- Protons have a positive charge
The Structure of an Atom
- In neutral (i.e. uncharged) atoms and objects the number of electrons and the number of protons are equal
The number of negative electrons in an atom balances the number of positive protons
The Direction of Forces
- When two charged particles or objects are close together, they also exert a force on each other
- This force could be:
- Attractive (the objects get closer together)
- Repulsive (the objects move further apart)
- 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
Opposite charges attract, like charges repel
Attraction or Repulsion Summary Table
- Attraction and repulsion between two charged objects are examples of a non-contact force
- This is a force that acts on an object without being physically in contact with it
Exam Tip
Remember the saying: “Opposites attract”.