Electricity Revision

ELECTRICITY

Aim: •Recognise that current will not flow around an incomplete circuit.

• Identify a range of materials that allow a current of electricity to flow around a circuit.

Complete and incomplete circuits

1. What happens to the bulb when the circuit

is complete?

The bulb lights up

2. Starting from the positive side of the cell, trace with your finger the path followed by the electricity as it flows around the circuit.

3. If you removed one of the wires to the left of the bulb. What happens to the bulb? The bulb would not light up 4. Again, starting from the positive side of the cell, try to trace the path the electricity should follow around the circuit.

5. If you were to reconnect the wire you removed and disconnected a wire which is to the right of the bulb What happens? The bulb would not light

up

Questions 1. What is a complete circuit?

2. What is an incomplete circuit?

3. What happens to the bulb when the circuit

is complete? Explain why this happens.

4. What happens to the bulb when the circuit is incomplete? Explain why this happens.

Questions 1.

What is a complete circuit?

A complete circuit is a complete loop with electricity flowing the way it's supposed to flow: from the battery, to the component, and back to the battery again.

1.

What is an incomplete circuit? An open circuit is a circuit where the path has been interrupted or "opened" at some point so that current will not flow

2.

What happens to the bulb when the circuit is complete? The current can flow and the bulb lights up.

3.

What happens to the bulb when the circuit is incomplete?

Explain why this happens. The path for the electrons to flow is broken, the current cannot flow so the bulb does not light up.

Copy and Complete Electricity is a flow of _____________ (negatively charged particles). Electricity can flow through____________ but not through _____________. ________ are good conductors of electricity.

Conductors

Insulators

Metals

Electrons

CIRCUIT DIAGRAMS, CELLS & BATTERIES Aim: •Show how to represent circuit components as symbols.

•Explain the role of cells and switches in circuits.

•Describe and understand the effect of adding cells in circuits

Circuit Symbols Voltmeter Ammeter

Variable Resistor Switch Bulb Motor

Cell Battery

Batteries and Switches

Questions: Q1. What happened to the brightness of the bulb when you add more batteries? Explain why The brightness increases because the current has increased.

Q2. What happens to the bulb in circuit D? Explain why.

The bulb will not light up, Cells must be connected the right way round if their voltages are to add up. If a cell is the wrong way around, then it will push against the others and we have to subtract its voltage.

MEASURING CURRENT IN SERIES CIRCUITS Aim: •Use an ammeter to measure current in a circuit •Describe the effect on current of adding more components in a circuit.

•Explain how a fuse works

The flow of current Current in a circuit is ____ used up. Current which leaves a cell returns to it. Current leaves from the ________ terminal and returns to the negative terminal.

The cell is a device which gives ________to components of the circuit. ___________ is what makes the current flow. A battery with a 9v rating will make the same lamp _________ than one with a 4.5v rating. energy

brighter positive

not

Voltage

Which fuse?

Very thin copper wire has a greater resistance than thicker copper wire. The thicker the wire the lower the resistance.

Complete the sentences: breaks melts protects If the current flow is too high then the wire in the fuse …… and ……….. The circuit. This ……… the device so that components themselves do not melt.

Fuse

5 amp

13 amp

Wire is… thicker / thinner thicker / thinner Resistance is… higher / lower higher / lower Used in… kettle / ipod kettle / ipod

Which fuse?

Very thin copper wire has a greater resistance than thicker copper wire. The thicker the wire the lower the resistance.

If the current flow is too high then the wire in the fuse melts and breaks the circuit. This protects the device so that components themselves do not melt.

Fuse

Wire is‌ Resistance is‌ Used in‌

5 amp

13 amp

thinner higher ipod

thicker lower kettle

SERIES AND PARALLEL CIRCUITS Aim: •Explain the features of series and parallel circuits.

•Build a complete parallel and series circuit

Credits!

Series Circuits

One The bulb will go out One Lamps or electrical appliances are connected in series, if one of the wires breaks, the appliance will not work.

Parallel Circuits

Three The other one remains lit Three The main lights are connected in parallel, if one goes out, the rest will remain lit

MEASURING CURRENT IN PARALLEL CIRCUITS Aim: •Use an ammeter to measure current in a parallel circuit •Explain how current behaves in a parallel circuit.

Circuit Blockbusters

Credits!

Summary

Measuring current in parallel circuits

The current would be the same!

Parallel circuits Current in a parallel circuit is ______ used up.

However it may not be the same everywhere you measure it. The current ________ when it comes to a branch. The ______ in the branches _______ up to the current ______ and returning to the ____________. battery not

current

splits up leaving

adds

CIRCUIT MODELS

Aim: •Use analogies to explain how electrical circuits work •Create your own analogy to explain how circuits work.

What is the missing current reading?

1

A1

2

A4

4

A2 A3

3 A1 = 4 amps A2 = 3 amps A3 =

1 amp

A4 =

4 amps

Credits!

A circuit is like a central heating system in a house: low pressure

Boiler and pump

radiator

Flow of water

High pressure

There is a pump that pushes water round the system. The water everywhere starts to move AT THE SAME TIME

There are pipes that CARRY the water.

In the pipes the water is FLOWING.

An electrical circuit is very similar to a central heating system.

The bulb in the circuit is like a radiator. An electrical device uses electrical energy supplied by the circuit.

battery

wires lamp

Instead of a flow of water, electricity flows in an electrical circuit.

The wires are like pipes; they carry the electricity round the circuit.

This is called the electrical current.

The electrical current is pushed by the battery, which has the same function as the pump and boiler.

The strength of push provided by the battery is called its voltage.

A circuit model

Circuit Models

RESISTANCE

Aim: •Describe what produces resistance in a circuit •Explain what effect resistance has on current.

Resistance

The current reducesf As the number of components increases, the resistance within the circuit also increases The brightness reduces each time a bulb is added as the resistance within the circuit increases.

Variable Resistors

Variable resisters increase the resistance within a circuit, if the resistance is increased the brightness of the bulb decreases, if it is decreased the brightness of the bulb increases.