Electric Charge: The Basics of Matter and Electricity

Terminology

Everything around you is matter: the device you’re reading this on, the table, the floor, the walls, the air. Matter is the “stuff”. And all matter has charge. It’s a property (characteristic) of matter. Mass is also a property of matter. Just like one of your characteristics is your eye colour or your height.

Gravity creates a force on matter because it has mass (which allows you to stay on the earth as it spins and not be flung into space). Charge also experiences a force when it is placed inside an electromagnetic field (combination of electric field and magnetic field).

Attraction and repulsion

Charge can be positive, negative (or neutral!). When we zoom in to a smaller part of matter – the atom – we can see where this comes from.

• Neutrons don’t have a charge – they are neutral.

• Electrons have a negative charge -1.6×10^-19 C (very small negative number)

• Protons have positive charge +1.6×10^-19 C (very small positive number)

Charge is measured in Coulombs (C).

Ever heard the phrase “opposites attract”? Well, it applies here. Unlike (opposite) charges attract, and like (the same) charges repel.

If the charges are closer together, they will repel / attract with more force. If they are further away, this is a weaker force (the size of the arrow on the diagram shows how strong the force is: longer arrow = stronger force)

Charging a body

Most objects have an equal number of electrons and protons, so it is neutrally charged. But you can “charge” it by removing or adding electrons.

Have you ever played around with a balloon and then it becomes “stuck” to your hair? This is because you charged the balloon – the electrons moved from your hair to the balloon. So now the balloon is negatively charged, and your hair is positively charged. Opposites attract, so the balloon is now “attracted” to your hair.

So, what is happening…?

Rubbing two objects (friction) can transfer free electrons between 2 materials. This is called charging a body (object). And static electricity is when objects “stick together” because they have more or less electrons than usual (they are charged). This is also what happens when you get “shocked” by  a trampoline or by a carpet – the charge builds up so much because of friction and then it creates a static shock.

Only the electrons get transferred – not the protons.

Static electricity just means it involves electrons, but the electrons aren’t moving through a circuit like with normal electricity.

You can charge something by conduction (2 objects touch each other), or by friction:

Electric fields

Remember how charges can be attracted or repelled by each other? We can actually predict how they will move! This is what electric field lines are.

Whenever there is a charged particle (positive or negative), there is an electric field. Because any other particle comes close to it, it will experience a force (attract / repel) depending on the charge. The electric field lines are imaginary lines that show how the charges will move.

If we take a positive or negative point charge, the electric field is lines flowing in or out of the charge. To determine the direction of the arrows, we pretend to take another positive charge and think about what direction it would move. For the positive point charge, the second positive charge would move away / outwards because it is repelled. For the negative point charge, the other positive charge would move towards it / inwards because it is attracted.

Okay, but what if we have a bunch of charge on a flat object? Let’s consider 2 of these: parallel plates, one positively charged, one negatively charged. Because they are equally spaced apart everywhere along the plate, the electric field will just be straight lines from the positive side to the negative side.

If you took a positive charge and put it anywhere inside the electric field, it would move away from the positive plate and towards the negative plate in a straight line.

What is electricity actually?

Electricity is just electrons flowing. This happens continuously in a loop to create a circuit.

Usually, we use metals like copper wires for electricity because they are conductors. Conductors are materials through which electrons can flow. But if we had bare copper wires in our house with electricity flowing through them, this would be very dangerous. So, we use materials like plastic to cover it. This is an example of an insulator which electrons (electricity) can’t flow through. Good insulators are materials like glass, plastic, rubber, air and wood.

Fun fact: Electricity can flow through water too!
(Water is a conductor)
That’s why you should keep any electrical equipment / devices away from water…

So, that’s the basics of what charge is, how it works and how this relates to electricity. There are more details about the electricity unit in some of the notes below: