Download Electricity powerpoint File

Objectives
Demonstrate the requirements for an electrical circuit that works.
Use a multimeter effectively to measure voltage and current in a simple
circuit.
3. Recall the symbols used in simple circuits. (cell, battery, power pack,
lamp, wire, switch, ammeter, voltmeter.)
4. Draw a circuit diagram from an actual circuit, or a picture.
5. Construct a circuit from a circuit diagram.
6. Use the terms series and parallel correctly.
7. Describe a circuit from a physical circuit or a circuit diagram using
correct terminology and construct or draw a circuit from a description.
8. Relate power (brightness etc.) to voltage and current in a working
circuit.
9. Calculate resistance from voltage and current.
10. Recognise the main features of a domestic electrical system in terms of
1-8
11. Recall the main features of the NZ electrical supply system in terms of
its sustainability.
1.
2.
Electrical symbols
wire
power pack
Draw all wires with a ruler. Make all corners right-angles.
Wires come out opposite sides of components (two wires only)
Power packs
Lab power packs are best used on DC
Watch for the overload light!
Lamps and wires
Make it glow
 Using wires, a lamp and a power pack, connect them
together in as many different ways as you can.
Note which sockets are used on the power pack and
lamp in the circuits that worked.
Why did some circuits work and others not?
Electrical circuits
An electrical circuit must have:
1. A supply of electrical energy
(eg a battery or power pack)
2. A complete pathway (eg wires
connecting all components)
3. A user of electrical energy
(eg lamp or heating coil)
Making measurements.
Meters are used to measure voltage and current.
 Multimeters
Analogue meters
Multimeter as a Voltmeter
The multimeter can be used to measure many things.
To measure voltage put leads in the holes marked “COM” and V
Turn the switch to the highest reading you might get.
The reading on the screen is in volts (V).
Voltmeters in circuits
 Voltmeters are used to measure voltage in a circuit.
 Voltage is a measure of how much energy is being
supplied or used in a circuit, so we connect a
voltmeter around something that is supplying (egpower pack) or using energy (eg- lamp) in the
circuit.
 Always check that the + terminal of the voltmeter
leads back to the + terminal of the power pack or it
will give a negative reading.
Measuring voltage in a circuit
Using the circuit with the power pack and one lamp:
 Connect leads from the voltmeter to every pair of points:
AB, BC, CD, AD
 Record the readings.
 Can you explain why you got these readings?
Ammeters in circuits
 Ammeters are used to measure current in a circuit.
 Current is the amount of electrical charge flowing in
a circuit every second. It is measured in units called
amps.
 Ammeters are always connected into the circuit so
that the current flows through them and can be
measured.
 Always check that the + terminal of the ammeter
leads back to the + terminal of the power pack or it
will give a negative reading.
Multimeter as an Ammeter
Put the leads in the holes marked COM and 10A
Set the switch to 10A DC. The reading is in amps (A)
Pull the circuit apart at the point where you want to measure and insert the meter
Measuring Current in a circuit
 Set up a simple circuit with a powerpack at 12 v and a lamp.
Connect the ammeter into different places in the circuit.
 What do you notice about the ammeter readings?
 Draw a circuit diagram and record the reading.
 Reduce the voltage on the power pack and measure the
current at different voltages. Record your results:
voltage
current
 Can you see any pattern connecting voltage and current?
 What happens to the brightness of the lamp as you change
the voltage?
Series circuits
 In a series circuit, the components are all connected
one after the other. There is only one pathway for the
current to flow.
 This circuit shows a battery, ammeter and two lamps
all connected in series.
1 bulb
2 bulbs in series
2 bulbs and an ammeter in series
Current in series circuits.
 Construct a circuit that has one lamp and an ammeter in
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series and connected to a power pack set at 12 volts.
Draw a circuit diagram of the circuit you have made.
Record the ammeter reading on your circuit diagram and
note the brightness of the lamp.
Now connect a second lamp in series into the circuit.
Draw a circuit diagram of this circuit.
Connect an ammeter in series with each lamp in turn so that
you are measuring the current in different parts of the
circuit.
Record the ammeter reading alongside each lamp and note
the brightness of the lamps.
Predict what will happen to the brightness and ammeter
readings when you add a third lamp in series. Test it out and
record your results.
Voltage in series circuits
Construct the circuit below:
Move the voltmeter to each lamp in turn.
Copy the circuit diagram and record the readings.
Unscrew one of the lamps from its socket. What happens to
the other lamps? What happens to the voltmeter reading?
Series circuits - summary
 There is only ___ pathway for the
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________ to flow.
As more lamps are added in series,
the lamps become ________.
If one lamp breaks all of the lamps
will ____ _____ because the circuit
is ______ .
The _______ is the same in all parts
of the circuit.
As more lamps are added in series,
_____ current flows.
The _______ is not the same in all
parts of the circuit.
As more lamps are added in series,
they ______ the voltage. This is why
the lamps become _________.
A1
A3
A2
Parallel circuits
 In a parallel circuit
there is more than one
pathway for the current
to flow.
Two
pathways
A
Quick Quiz on drawing circuits:
Draw a series circuit with two cells, three lamps
and an open switch.
2. Draw a parallel circuit with a battery, two lamps
in parallel and one lamp in series in the main
part of the circuit.
3. Draw a circuit with a cell, open switch, lamp and
fuse in series and a second lamp in parallel with
the first lamp.
4. Draw a circuit with three cells, an open switch,
an ammeter and two lamps in series.
1.
Answers
1.
3
2.
4
A
Making a parallel
connection
2 bulbs in parallel
Construct the circuit.
Draw the circuit.
Current flow in parallel circuits
Investigation 1:
 Connect a powerpack (12v), an ammeter and a lamp all
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in series. Note the ammeter reading.
Place another lamp in parallel around the first lamp.
What happens to the ammeter reading?
What do you think will happen to the ammeter
reading when you add a third lamp in parallel around
the second lamp? Test it out.
Draw a circuit diagram for the circuit you have made
with the powerpack, ammeter and the 3 lamps in
parallel.
Describe what happens to the current flow as more
lamps are added in parallel in a circuit.
Current flow in parallel circuits
Investigation 2:
 Construct a circuit having 3 lamps in parallel with one
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another and the power pack.
Put an ammeter between the powerpack and the
circuit.
Put an ammeter between the joined plugs and the
lamp. Repeat for each lamp.
Draw a circuit diagram to show the 3 lamps in parallel
and an ammeter in each of the positions you have
tested.
Record all the currents on the ammeters.
Is there a pattern to the readings?
Voltage in parallel circuits
 Construct a circuit with a powerpack and 3 lamps in
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parallel with each other.
Test the voltage across each lamp in turn and the
voltage across the powerpack.
Compare the readings.
Draw a circuit diagram to show the powerpack , 3
lamps in parallel and a voltmeter in parallel around
each of the components you have tested.
Record the voltages on the voltmeters.
What pattern do you see?
Lamp brightness in series and parallel circuits
1) Set the powerpack at 12V
2) Set up two bulbs in series and compare the brightness
of the bulbs to the same two bulbs in parallel
3) Which bulbs have the higher potential difference?
Those in series or parallel
The brightness of a lamp depends on the power.
Energy changes/transformations
Energy is not created or destroyed but it
can be changed (transformed) from one
form to another.
This is called the ‘law of conservation’
Energy changes in an electrical circuit
Match the diagrams to the energy change
statement that best matches them.
1) Electrical energy to heat energy
2) Electrical energy to light energy
3) Electrical energy to kinetic, sound and heat
energy
4) Electrical energy to kinetic energy
Homework exercise
Choose an electrical appliance at
home. Discuss the energy changes in
the appliance.
Power
The rate at which energy is changed by a
device is called its POWER.
The power is measured in watts (W)
(look at an implement to see if you can find
the power rating in W written on it)
Power is decided by both voltage (V)and
current (I).
P=Vx I
Conductors and Insulators
Conductors
 These materials allow current to flow easily.
We use these materials in electrical circuits.
Metals are good conductors.
Insulators
 Insulators don't allow current to flow easily and we use
these materials to protect ourselves. Wood, glass and plastic
are examples of good insulators.
Resistance
 Resistance is a measure of how poor a conductor is.
 Resistance of a conductor is the ratio of potential
difference across the conductor to the current
through the conductor. i.e.R=V/I
 Resistance is the opposition to electrical current.
i.e. How much voltage is needed to get a given
current.
 Resistance is measured in units called ohms (W)
 Using a multimeter, calculate the resistance of a
variety of objects.