Simple Electric Circuits D. Crowley, 2008. Simple Electric Circuits To be able to draw simple electric circuits and know what happens when more bulbs.

Simple Electric Circuits

D. Crowley,

2008

Simple Electric CircuitsTo be able to draw simple electric circuits and know what happens when more bulbs are added

Wednesday, April 19, 2023

Electricity

What is electricity?

Electricity is the flow of electrical power (charge) in the form of electrons

Electricity is a useful secondary energy source – most energy sources (like coal, oil, nuclear, wind etc…) can be converted into electricity

Electricity is the flow of electrons around our electrical circuit

CircuitsAn electric circuit is like the central heating system in a house…

There is a pump which pushes water all around the house

The water everywhere starts to move at the same time

There are pipes which carry the water

In the pipes the water is flowing

When river water moves, we say that a current of water flows - when electric charges move in a wire, we say that an electric current flows

boilerand

pump

radiator

highpressure

lowpressure

flow ofwater

radiator

CircuitsA bulb in the circuit is like a radiator – an electrical device uses electrical energy, supplied by the circuit

The wires are like pipes - they carry the flow of electricity (current) around the circuit (flow of electrons goes from negative to positive)

The electrical current is pushed by the cell (battery) – this is the voltage

+ -

Cell

Wires

Lamp

Electric CircuitsAn electric current needs two things: -

Something to make the electricity flow (e.g. a battery or power pack)A complete circuit

Without these two basic things, an electric current will not flow

+ -

Cell

Wires forming a complete circuit

Component DiagramsCircuit symbols are used to show the components in an electrical circuit (wires are represented by straight lines)

Current – the flow of electricity (flow of electrons) around the circuit

Voltage – the driving force which pushes the current around the circuit

Resistance – anything in the circuit which slows the flow down

Component SymbolsA common list of components is shown below – use this to complete the simple electric circuits worksheet

Simple Electric Circuits

Simple Electric Circuits

Switches

Switches are used to control components in circuits

In a simple circuit with one switch, the switch controls all the components…

Series & Parallel

There are two types of circuit – series and parallel

For now, we will concentrate on series circuits – circuits where all the components are connected in a line, end to end

Removing one component breaks the circuit, stopping all the components

Christmas tree lights are often in series, so when one bulb blows, they all stop

They are also used for warning systems, so if a component breaks the light in series will stop, hopefully alerting you

CurrentWhat is current?

Current is a measure of how much electric charge flows through a circuit (the flow of electrons around a circuit, from negative to positive terminals))

Current is measured in amps – e.g. 20A current is bigger than 5A current

To measure current in a circuit, the ammeter must be placed in series – it does not matter in what order you place this

CurrentTo measure the current, the ammeter must be placed in series (in any order)

+ -Ammeter

A

The ammeter can be placed after the components (lamp)

CurrentTo measure the current, the ammeter must be placed in series (in any order)

+ -

Ammeter

A

Or the ammeter can be placed before the component (bulb)

Experiment

Experimental Observations

Your first experiment is to find out what happens to the brightness of bulbs when you add more than one to a circuit

Firstly set up a circuit with one bulb in it, and note how bright it is – place the ammeter in different parts of the circuit, testing the current

+ - + -

A A

Experimental Observations

Secondly add a second bulb to the circuit and repeat the current test (place it in different positions

Then repeat this with three bulbs in the circuit

+ -

A

+ -

A

+ -A

Experimental Observations

Experiment with three bulbs in the circuit

+ -A

+ -

A

+ -A

+ -

A

Ammeter

Your second experiment is to find the current of each circuit

Reset your circuit to contain just one bulb, and connect the ammeter in series and record the amps reading

Then repeat this with two and three bulbs, recording each current reading

+ - + - + -1. 3.2.

A A A

Current

The current is not used up by the components in a circuit

The current is the same anywhere in a series circuit

+ - Current is the same, anywhere in the circuit

AA

Current is the same at this point in the circuit, e.g. 1A

Current is the same at this point in the circuit, e.g. 1A

Dimmer Bulbs

As more bulbs are added to the circuit they all get dimmer

As more bulbs are added the resistance increases, reducing the flow of current

Having a circuit with many bulbs in it causes a low current, but remember the current is still the same anywhere in this circuit+ -

A Current is always

1A, anywhere

in this circuit

+ -

A Current is reduced in this circuit (more

resistance) but it is still always 0.5A, anywhere in this

circuit

Current Summary

Circuit 1 – the current at different positions in the circuit, before and after the lamp was the __________

Current is __________ used by the components in the circuit

Circuit 2 – increasing the number of components in the circuit __________ the current

The current at all points in a series circuit is __________

Circuit 1

A A

Circuit 2

A A

A

Key words: same / decreased / same / not

same

not

decreased

same