## Akoranga 1 Mahi Tuatahi

On the board, brainstorm all the things you can remember about electricity from Year 10!

## Te Whāinga Ako

- Explain how static electricity is created by the removal or addition of electric charge (and is measured in Coulombs)

Write the date and te whāinga ako in your book

## Static Electricity

Static electricity has many effects - some dangerous, some hilarious, but they all depend on charge!

### Charges: Positive & Negative

From Year 10 we should all remember that, much like magnets, opposites attract and likes repel.

### Charge Carriers

Recall: **the atom**. What element is this? What are the three subatomic particles that make it up?

Draw this diagram in your book and label the particles and the charge they carry.

**Electrons**: Negatively charged**Protons**: Positively charged**Neutrons**: No charge

**Pātai**: What happens when an atom loses or gains electrons?

## Ions

- Electrons are extremely light and move very fast. Therefore they can sometimes escape an atom.
- An ion is formed when an atom gains or loses electrons.
- Losing one or more electrons makes you
**positively charged**and is called a**cation**. - Gaining one or more electrons makes you
**negatively charged**and is called an**anion**.

### Pātai Tahi

What did we do in Year 10 Pūtaiao to remove charges from one object and put them onto another?

#### Whakatika Tahi

We applied friction!

### Van der Graaf Generator

## Akoranga 2 Mahi Tuatahi

Working with the person next to you, describe the process of generating a spark using the Van der Graaff Generator. Start with the motor, the brush, the dome and then go to the wand and spark.

## Te Whāinga Ako

- Explain how static electricity is created by the removal or addition of electric charge (and is measured in Coulombs)

Write the date and te whāinga ako in your book

## What is Charge?

- In Physics the symbol for charge in equations is $q$ or $Q$.
**Unit**: Coulombs (C)- We use it to describe how positive or negative an object is.

### So, What is a Coulomb?

- We know that electrons are negatively charged. In fact, they have a charge of $-0.000,000,000,000,000,000,16C$
**Pātai**: Write this number in scientific form (e.g. $1\times10^{5}$)

- $-0.000,000,000,000,000,000,16 C =-1.6 \times 10^{-19}C$.
**Pātai**: How many times does this number fit into $1$? Therefore, how many electrons are needed to carry $1C$ of charge?

\begin{aligned} num_{e} &= \frac{Q_{total}}{q_{e}} \newline num_{e} &= \frac{1}{1.6 \times 10^{-19}} \newline num_{e} &= 6,250,000,000,000,000,000 = 6.25 \times 10^{18} \end{aligned}

$6.25 \times 10^{18} electrons = -1 C$

$1C$ is the amount of charge carried by $6.25 \times 10^{18}$ electrons.

### Pātai Rua

If a balloon has charge of $-3C$: did the balloon lose or gain electrons, and how many?

#### Whakatika

If a balloon has charge of $-3C$: did the balloon lose or gain electrons, and how many?

\begin{aligned} & \text{Negative C} \rightarrow \text{electrons gained (-ve charge)} \newline & num_{e} = 3 \times (6.25 \times 10^{18}) \newline & num_{e} = 1.875 \times 10^{19} && \text{ electrons gained} \end{aligned}

## Akoranga 3 Mahi Tuatahi

If Charlotte has charge of $0.2C$ did she lose or gain electrons and how many?

#### Whakatika

If Charlotte has charge of $0.2C$ did she lose or gain electrons and how many?

\begin{aligned} & \text{Positive C} \rightarrow \text{electrons lost (+ve charge)} \newline & num_{e} = 0.2 \times (6.25 \times 10^{18}) \newline & num_{e} = 1.25 \times 10^{18} && \text{ electrons lost} \end{aligned}

## Ngā Whāinga Ako

- Be able to define current
- Be able to calculate current using charge and time
- Recall the properties of conductors and insulators

Write the date and ngā whāinga ako in your book

## Charge and Current

- Current is the flow of charge (electrons, ions etc.)
- Like a river, current is the amount of charge passing a point each second
- Therefore we can simply give an equation relating the three like this:

\begin{aligned} current &= \frac{charge}{time} \newline I &= \frac{q}{t} \newline A &= \frac{C}{s} \end{aligned}

Alternative definition of a Coulomb:

A current of $1A$ will carry $1C$ of charge past a point in $1s$.

### Task/Ngohe

Worksheet One Q1-4

## Conductors

- A conductor is a material through which charge can move freely
- E.g. Metals because they have a
*delocalised sea of electrons*

# Insulators

- A material through which electrons cannot easily flow
- The electrons encounter a large friction force when trying to move
- This friction causes heat to build up
- e.g. Wood can catch fire if current is applied

### Task/Ngohe

Homework Booklet Q1a