# Electric Charge and Static Electricity

> Where electricity comes from. Charges, the electrostatic force, static shocks and lightning.

From HSC Physics on WhizzNotes, free study notes for NSW students: https://whizznotes.com/physics/electric-charge/. Updated 2 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: The balloon on the wall
At her little brother's birthday party, Grace rubbed a balloon on her hair. Her hair stood up and followed the balloon around like it was alive. Then she pressed the balloon against the wall and let go. It stayed there, stuck, for the rest of the party.

No glue. No tape. Just an invisible force.

That force is the same one that makes lightning crash across the sky, and the same one that holds every atom in your body together. It all comes from something called **electric charge**.

**In short:** Electric charge comes from protons (positive) and electrons (negative). Rubbing two objects moves electrons from one to the other, so one becomes negative and the other positive: this is static electricity. Like charges repel and unlike charges attract.

## Atoms and charge

Everything is made of **atoms**. Atoms contain three kinds of particles:

| Particle | Charge | Where |
|---|---|---|
| **Proton** | Positive (+) | In the nucleus (centre) |
| **Neutron** | No charge (neutral) | In the nucleus |
| **Electron** | Negative (−) | Moving around the nucleus |

A normal atom has the **same number** of protons and electrons, so the charges cancel. The atom is **neutral**.

Protons are locked in the nucleus. **Electrons are the ones that can move** from one object to another.

## Making static charge

When you rub two different materials together, **electrons are transferred** from one to the other.

- The object that **gains** electrons becomes **negatively** charged.
- The object that **loses** electrons becomes **positively** charged.

### Worked example: Grace's balloon
Rubbing the balloon on hair moves electrons **from the hair to the balloon**.

- Balloon: extra electrons, so **negative**.
- Hair: lost electrons, so **positive**.

Opposite charges attract, so the hair reaches towards the balloon. Each hair has the same positive charge, so the hairs repel each other and stand apart.

### Watch out: Positive charges do not move
An object becomes positive by **losing electrons**, not by gaining protons. In solids, only electrons move.

## The electrostatic force

Charged objects push or pull each other without touching. This is the **electrostatic force**, a non-contact force.

- **Like charges repel**: + and +, or − and −.
- **Unlike charges attract**: + and −.
- A charged object can also attract a **neutral** object. The balloon pushes the wall's electrons slightly away, leaving the nearby surface a bit positive. Then the negative balloon is attracted to it.

The force is **stronger** when the charges are **bigger** and when the objects are **closer**.

## Conductors and insulators

- **Conductors** let electrons flow through them easily: metals (copper, aluminium), graphite, salty water, the human body.
- **Insulators** do not let electrons flow: plastic, rubber, glass, wood, dry air.

Static charge builds up on **insulators**, because the charge cannot flow away. If you rub a metal rod while holding it, the charge flows through you into the ground. This is called **earthing**.

## Static electricity in real life

- **Shocks**: walking on carpet charges you up. Touching a metal door handle lets the charge jump. Zap.
- **Lightning**: ice and water bumping inside storm clouds separate huge amounts of charge. When it gets big enough, it jumps to the ground as a giant spark.
- **Fuel tankers** are earthed while refuelling, so a spark cannot ignite the fuel.
- **Useful**: photocopiers, laser printers and spray painting cars all use static charge.

**Mind map**

```text
Electric charge
  Atoms
    Protons +
    Electrons −
    Neutrons 0
  Charging
    Rubbing moves electrons
    Gain electrons: negative
    Lose electrons: positive
  Force
    Like charges repel
    Unlike charges attract
    Closer = stronger
  Materials
    Conductors: metals
    Insulators: plastic, rubber
    Earthing
  Real life
    Shocks
    Lightning
    Printers
```

### Year 11: Charge and electric fields
Charge is measured in **coulombs (C)**. One electron has a charge of

$$e = -1.6 \times 10^{-19} \text{ C}$$

So one coulomb is about $6.25 \times 10^{18}$ electrons.

An **electric field** is the region where a charge feels a force. The field strength is the force per unit charge:

$$E = \frac{F}{q}$$

Field lines point from **+ to −** (the way a positive charge would be pushed). Between two parallel plates the field is uniform: $E = \dfrac{V}{d}$.

### Year 12: Coulomb's law
The force between two point charges $q_1$ and $q_2$ a distance $r$ apart is:

$$F = \frac{1}{4\pi\varepsilon_0}\frac{q_1 q_2}{r^2} = k\frac{q_1q_2}{r^2}$$

where $k \approx 9.0 \times 10^9 \text{ N m}^2 \text{ C}^{-2}$. Like gravity, it is an inverse square law. Unlike gravity, it can **repel** as well as attract, and it is enormously stronger. The electric force between two protons is about $10^{36}$ times bigger than the gravity between them.

A charge moving through a potential difference $V$ gains energy $W = qV$. This is how particle accelerators and old TV tubes speed up electrons.

## Quick summary

- Atoms contain positive protons, negative electrons and neutral neutrons.
- Only **electrons** move between objects.
- Gain electrons: negative. Lose electrons: positive.
- Like charges repel. Unlike charges attract. Closer means stronger.
- Conductors let charge flow. Insulators do not, so static builds up on them.
- Lightning and static shocks are sudden flows of built-up charge.

## Quiz

Try these questions from the chapter quiz.

1. Which particle moves when objects become charged by rubbing?
   - A. Proton
   - B. Neutron
   - C. Electron
   - D. Nucleus
   - Answer: C. Electron. Electrons are on the outside of atoms and can be transferred.

2. A plastic rod gains electrons when rubbed with a cloth. The rod becomes:
   - A. Negatively charged
   - B. Positively charged
   - C. Neutral
   - D. Magnetic
   - Answer: A. Negatively charged. Electrons are negative, so gaining them makes the rod negative.

3. In the example above, the cloth becomes:
   - A. Negatively charged
   - B. Positively charged
   - C. Neutral
   - D. Hot only
   - Answer: B. Positively charged. The cloth lost electrons, so it has more protons than electrons.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/physics/electric-charge/#quiz