BASIC ELECTRICITY

Nicola Tesla: Mad Electricity

LESSON 1 : CIRCUIT SYMBOLS

Draw and identify the circuit symbol for a battery, lamp, switch, resistor, motor, and variable resistor.

State that lamps, heaters and motors and buzzers convert electrical energy into other forms.

LESSON 1 : CIRCUIT SYMBOLS

Examine examples of circuit components and produce a poster matching pictures of components to their symbols and energy conversions.

ELECTRICAL ENERGY CONVERTERS

Loudspeaker Microphone Hair straighter TV Lift going up

Heater Lamp

electrical sound sound electrical electrical heat electrical sound + light electrical kinetic +

potential electrical heat electrical light + heat

What are the energy conversions associated with each of these devices?

Now watch this short video: Electricity and circuits

LESSON 2/3: PRACTICAL CIRCUITS - QUIZ BOARD

LESSON 2/3: PRACTICAL CIRCUITS - TRAFFIC LIGHTS

LESSON 2/3 – PRACTICAL CIRCUITS - ELECTROPLATING

LESSON 4,5 ELECTRICAL MEASUREMENTS IN CIRCUITS

State that an ammeter is used to measure current in Amps. Draw and identify the circuit symbol for an ammeter. Draw a circuit diagram showing the correct position of an

ammeter in the circuit. State that current is a flow of charge and is measured in

amperes State that an voltmeter is used to measure voltage in Volts Draw and identify the circuit symbol for a Voltmeter. Draw a circuit diagram showing the correct position of a

voltmeter in the circuit. State that voltage is the electrical push and is measured in

Volts. State that the voltage is the same for all components

connected in parallel.

LESSON 4 : ELECTRICAL MEASUREMENTS –SERIES CIRCUIT – XMAS TREE LIGHTS

Xmas tree lights are wired in series – in a line one after the other.

Connect three bulbs in series as shown in the diagram.Use retort stands as model tree!

You will need:• Connecting wire• 3 x Bulb holders with 2.5v lamps• 6V battery• 1 x retort stands and clamps• Wire strippers

MEASURING CURRENTS IN THE CIRCUIT

Watch as you are shown how to measure the currents in the circuit you have just built.

Now go and measure the currents from the battery and through each of the lamps.

Can you notice a pattern? The current is the same at all

points at all points in the circuit

video clip: How to use a multimeter

What is current? Programs / Virtual Int1 Physics / Practical Electricity / Current

MEASURING CURRENT Current is the flow of tiny electric charges around a

circuit. An ammeter is used to measure the current through a

circuit, measured in amperes (A) To connect an ammeter we have to break the circuit and

put the ammeter in series with the other components. The size of a current in a series circuit is the same at

all points in the circuit

?A?A

?A

2A2A

2A

MEASURING VOLTAGES IN THE CIRCUIT Watch as you are shown

how to measure the voltages in the circuit you have just built.

Now go and measure the voltages across the battery and each of the lamps.

Can you notice a pattern?

The voltages in a series circuit add to equal the battery voltage (or very similar!)

MEASURING VOLTAGE IN SERIES

Voltage can be thought of as the 'push' it exerts on charges in the circuit. A bigger voltage means a bigger 'push', resulting in a larger current

A voltmeter is used to measure voltage, in volts (V) Voltmeters are connected in parallel to either side of the

component. The size of the voltage across the battery in a series circuit is

equal to the sum of the voltages across the other components.

?V?V ?V

6V3V 3V

LESSON 5 : ELECTRICAL MEASUREMENTS IN A PARALLEL CIRCUIT – STREET LIGHTS

Street lights are wired in parallel and are controlled by a time switch driven by a clock. This turns the lights on and off at the correct time.

Connect three bulbs in parallel as shown in the diagram.Use retort stands as model lamp posts.

You will need:• Connecting wire• 3 x Bulb holders with 6v lamps• 6V battery• 3 x retort stands and clamps• Wire strippers

• What are the main advantages of wiring street lamps in parallel?

MEASURING VOLTAGES IN THE CIRCUIT

Watch as you are shown how to measure the voltages in the circuit you have just built.

Now go and measure the voltages across the battery and each of the lamps.

Can you notice a pattern?

The voltages in a parallel circuit are all the same (or very similar!)

MEASURING VOLTAGE The size of the voltage across the battery in

a parallel circuit is equal to the voltages across the other components.

?V ?V ?V6V 6V 6V

MEASURING CURRENTS IN THE CIRCUIT

Watch as you are shown how to measure the currents in the circuit you have just built.

Now go and measure the currents from the battery and through each of the lamps.

Can you notice a pattern? In a parallel circuit the

current from the battery equals the sum of the currents through the lamps (or very similar!)

MEASURING CURRENT IN A PARALLEL CIRCUIT In a parallel circuit:

the size of the current from the battery equals the sum of the currents through each of the other components.

?A ?A ?A

?Avideo clip: Lighting Circuit

4A 2A 2A

4A

ADVANTAGES OF WIRING STREET LAMPS IN PARALLEL:

When bulbs are connected in parallel each bulb gets the full battery voltage.

Each bulb lights with equal brightness. If one or more bulbs stop working or are removed the

rest continue lighting.

SERIES V PARALLEL SHOW-ME EXERCISE You will see statements appear that may apply to

SERIES circuits or PARALLEL circuit. Which is it?

SERIES PARALLEL

These have no branches or junctionsIf one bulb breaks, the

other bulbs in other branches stay on.

Can be turned on and off by a single switch anywhere in circuit

If you put more bulbs in they will be dimmer as it is harder for the current to get through- the resistance is higher

Switches can be put into the circuit to turn on and off all or part of the circuit.

The sum of voltages across all the components is equal to the voltage across the cell or battery

These have branches and junctionsIf one bulb breaks, all the others go out.If you put more bulbs

in they will stay brightThe size of current flowing in different parts of the circuit can be different.

AMMETER AND VOLTMETER EXERCISES Redraw each of the following diagrams and on each,

Add a meter to find the voltage across component E Add a meter to find the current through component F

Now complete the exercise, “Measuring current and voltage in series and parallel circuits”

CURRENT AND VOLTAGE CLIPS

Current and voltage in a circuit. Current and Voltage in a series and parallel ci

rcuit

LESSON 7/8: OHM’S LAW - RESISTANCE

Conduct an experimental investigation of the relationship between voltage and current through a resistor.

State that voltage/current = constant State that the “constant” is called the

“resistance” State that resistance is a measure of the

opposition to the flow of current in a circuit. State that resistance = voltage/current is

called Ohm’s law. Calculate resistance using Ohm’s law

INVESTIGATION: HOW DOES CHANGING THE VOLTAGE AFFECT THE CURRENT ?

In this experiment you will use battery voltage to push current through a resistor.

You will use an ammeter and a voltmeter to find how changing the voltage affects the current.

Follow the instructions on the worksheet, “Voltage, Current and Resistance”

OHMS LAW 2

Number of

batteries

Voltmeter reading(Volts)

AmmeterReading(Amps)

1

2

3

4

current

voltage

OHM’S LAW - RESISTANCE

An experimental investigation of the relationship between voltage and current through a resistor shows that voltage/current = constant.this is called Ohm’s Law

The “constant” is called the “resistance”.

Resistance is a measure of the opposition to the flow of current in a circuit.

Calculate resistance using:

CALCULATING RESISTANCE FROM AMMETER AND VOLTMETER VALUES

12V

0.1A

resistance =

voltage

current

Example:

The current through a resistor is 0.1 amperes when the

voltage across it is 12 volts. Calculate the resistance.

resistance =voltage

current

12

0.1= = 120W

OHMS LAW PRACTICE1. A resistor has a voltage across it of 12 volts and a current

through it of 2.5 amperes. Calculate the resistance of the resistor. Solution

2. A voltage of 6 volts is across a resistor where the current is 0.5 amperes. What is the value of the resistor? Solution

3. Calculate the resistance of a component when a voltage of 24 V causes a current of 0.1 amperes. Solution

5. A torch bulb is marked "6 V, 0.25 A".Calculate the resistance of the bulb. Solution

Practical Problems involving resistance

Beath High School - Int 1 Physics 29

1. A resistor has a voltage across it of 12 volts and a current through it of 2.5 amperes.Calculate the resistance of the resistor.

resistance =voltage

current

12

2.5=

4.8 W=

2. A voltage of 6 volts is across a resistor where the current is 0.5 amperes.What is the value of the resistor?

resistance =voltage

current

6

0.5=

12 W=

3. Calculate the resistance of a component when a voltage of 24 V causes a current of 0.1 amperes.

resistance =voltage

current

240.1

=

240 W=

4. A torch bulb is marked "6 V, 0.25 A".Calculate the resistance of the bulb.

resistance =voltage

current

6

0.25=

24 W=

LESSON 9: PRACTICAL PROBLEMS INVOLVING RESISTORS

Draw and identify the circuit symbol for a resistor and a variable resistor.

State that resistors convert electrical energy into heat energy.

State that an ohmmeter is used to measure resistance.

State that resistance is measured in ohms. State that an increase in resistance of a

circuit leads to a decrease in the current in the circuit.

Give two practical uses of resistors.

PRACTICAL USES OF RESISTORS 1

The most common use for a resistor is simply to control the size of the current flowing in part of a circuit.

The larger the resistance the smaller the current. The smaller the resistance the larger the current.

Resistance is measured in units of ohms (Ω)

Symbol for resistor:

Symbol for variable resistor:

PRACTICAL USES OF RESISTORS 2

Dimmer Switch Fan Speed Scaletrix controller Petrol Gauge Heating Element Radio volume control Skin Resistance – Lie Detector