Electric Charge
Physics: IB Diploma Higher Level, topic 4.5.1
Electrical Charge
Objects become charged when they gain or lose electrons. Charge is measured in Coulombs (C).
Like charges repel
- An object can be positively charged or negatively charged.
- Like charges repel each other.
- Two positive charges will repel each other.
- Two negative charges will also repel each other.
Unlike charges attract
- Unlike charges attract each other.
- A negative charge and a positive charge attract each other.
Charging an Object
Objects become charged by gaining or losing electrons.
Losing/gaining electrons
- Electrons are negatively charged.
- An object that loses electrons becomes positively charged and an object that gains electrons becomes negatively charged.
Sparks
- When there is a difference between the positive and negative charge of two objects, there is a potential difference between the two objects. This potential difference causes a rapid transfer of charge. Energy is stored in an electrostatic store and a spark is produced.
- In clouds during a storm, charge builds up and creates lightning, which is an example of a spark.
Charged Objects
Charged objects can exert forces on other objects.
Friction
- Applying friction to an object against another object can cause electrons to jump from one object to the other. This causes both objects to become charged.
Charged rod
- A plastic rod (or a balloon) can be charged by rubbing it with a cloth (or hair).
- The charged rod will attract a gentle stream of water falling from a tap.
- The charged rod can move an empty aluminum soda can. The charge on the rod attracts or repels the electrons in the metal, moving the can.
Isolated objects
- Conductors allow charge to flow to earth, so they would not maintain (keep) this charge.
- We call objects with no conducting path (link) to earth isolated objects.
Test yourself on Electric Charge
Which charges will repel each other?
Which of the following are true of electric charges?
What are the units of charge?
Which of the following are true of any material?
What charge will a material gain if it loses electrons?