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NAME : ...............................................
TEACHER : ..........................................
XXX SCHOOL
PHYSICS
Unit 1 2013
Electricity
VCE PHYSICS UNIT 1 - ELECTRICITY
RESISTOR COLOUR CODE
RESISTORS USED IN ELECTRONIC CIRCUITS ARE SO SMALL THAT IT IS DIFFICULT TO LABEL
THEM WITH THEIR RESISTANCE VALUE. INSTEAD, A COLOUR CODE IS USED, GIVING NOT ONLY
THE RESISTANCE, BUT ALSO THE ACCURACY OF THE STATED VALUE OF THE RESISTOR (ITS
TOLERANCE).
THE
FIRST COLOURED BAND GIVES THE VALUE OF THE FIRST DIGIT, THE SECOND BAND THE
SECOND DIGIT. THE THIRD BAND INDICATES THE NUMBER OF ZEROS THAT ARE TO BE ADDED
TO THE FIRST TWO NUMBERS TO GIVE THE VALUE OF THE RESISTANCE (IN OHMS). THE FORTH
BAND SHOWS WHETHER THE VALUE OF ACTUAL RESISTANCE IS WITHIN 5% OR 10% OF THE
STATED VALUE.
1ST COLOUR BAND
1ST DIGIT
BLACK
0
BROWN
1
RED
2
ORANGE
3
YELLOW
4
GREEN
5
BLUE
6
VIOLET
7
GREY
8
WHITE
9
EXAMPLE:
2ND COLOUR BAND
2ND DIGIT
BLACK
0
BROWN
1
RED
2
ORANGE
3
YELLOW
4
GREEN
5
BLUE
6
VIOLET
7
GREY
8
WHITE
9
GREEN
3RD COLOUR BAND
4TH COLOUR BAND
NUMBER OF ZEROS
TOLERANCE
BLACK
NO ZEROS
BROWN
ONE ZERO
RED
TWO ZEROS
GOLD
ORANGE
THREE ZEROS
SILVER
YELLOW
FOUR ZEROS
GREEN
FIVE ZEROS
BLUE
SIX ZEROS
VIOLET
SEVEN ZEROS
GREY
WHITE
BLUE ORANGE
SILVER
ST
1 COLURED BAND: GREEN (5)
2ND COLOURED BAND: BLUE (6)
3RD COLURED BAND: ORANGE (THREE ZEROES)
R = 56 000  = 56 K
Page 2
EIGHT ZEROS
NINE ZEROS
5%
10%
VCE PHYSICS UNIT 1 - ELECTRICITY
Index
Page
Introductory Notes On Electricity
4
Connecting Meters
5
Expt 1: Voltage Drops Around a Circuit
5
Expt 2: Converting Electrical Energy into GravitationalPotential Energy
8
Voltage - Current Characteristics
10
Expt 3: Ohmic Resistors
10
Expt 4: Series & Parallel Circuits
12
Expt 5: Resistance of a Light Globe Filament
16
Expt 6: The Diode
18
Expt 7: The Light Dependent Resistor
20
Expt 8: The Thermistor
22
Expt 9: Household Electricity Supply
23
Article of Solar Cells
27
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VCE PHYSICS UNIT 1 - ELECTRICITY
INTRODUCTORY NOTES ON ELECTRICITY
This topic should take about four weeks.
The Central Ideas of this topic are:
The use of electricity underpins much of the structure of our lives. Safe and effective use
of electricity is important for individuals and the community generally. Much of our
present use is explained by basic DC (Direct Current) circuit theory. This area of study
will include:
Key knowledge
• apply the concepts of charge (Q), electric current (I), potential difference (V), energy (E) and
power (P), in electric circuits
• analyse electrical circuits using the relationships I = Q/t, V = E/Q, P = E/t = VI, E = VIt
• model resistance in series and parallel circuits using
– potential difference versus current (V-I) graphs
– resistance as the potential difference to current ratio, including VI = R = constant for ohmic
devices
– equivalent effective resistance in arrangements in
• series: RT = R1 + R2 + ... + Rn and
• parallel: 1/RT = 1/R1 + 1/R2 + .... + 1/Rn
• model simple electrical circuits such as car and household (AC) electrical systems as simple direct
current (DC) circuits
• model household electricity connections as a simple circuit comprising fuses, switches, circuit
breakers, loads and earth
• identify causes, effects and treatment of electric shock in homes, relating these to approximate
danger thresholds for current and time
• investigate practically the operation of simple circuits containing resistors, variable resistors,
diodes and other non-ohmic devices
• convert energy values to kilowatt-hour (kWh)
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VCE PHYSICS UNIT 1 - ELECTRICITY
Connecting Meters
Note: The meters have several ranges to measure small, medium and large
values of current and voltage. The meters are most sensitive of the lowest
range. If a large current or voltage is applied to the meter when it is on this
range, it will be damaged.
When connecting a meter into a circuit ALWAYS always start on the least
sensitive range and then adjust the range if needed.
a)
The Voltmeter
The voltmeter measures the energy lost by the charge as it moves through a section of the
circuit. For this reason, the voltmeter is connected across the section.
Positive or
Red
Resistor
V
Note: the Positive or Red terminal of the meter must be connected onto the
circuit so that it runs around to the Positive or Red side of the battery or power
supply.
b)
The Ammeter
The ammeter measures the current going through a section of the circuit. That is, all the
current that goes through the section must go through the ammeter. For this reason the
ammeter is placed in the circuit.
Note: the Positive or Red terminal of the meter must be connected into the
circuit so that it runs around to the Positive or Red side of the battery or power
supply.
c)
What does a battery do?
A battery is a source of energy. A 6 volt battery gives 6 joules of energy to each coulomb
of charge that leaves the battery. This energy is used up as the charge goes around the
circuit.
In some sections of the circuit the charge loses little energy as it goes through the section.
In this instance an voltage reading across the section would read very close to zero, even
though there is current flowing through the section.
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #1
VOLTAGE DROPS AROUND A CIRCUIT
In this experiment you will investigate how the voltage changes as the current passes through
various components that make up a circuit.
Theory
You will need to understand the meaning of voltage and current as they relate to charge, the
meaning of electromotive force of a battery, and be able to connect an ammeter and voltmeter
correctly.
Equipment
• a 6 volt battery,
• two 12 ohm resistors,
• connecting wires.
•
•
•
a voltmeter,
a circuit board,
an ammeter
•
a switch.
Your task will be to construct various circuits and measure voltages and the current.
Procedure
1.
Connect up the circuit shown.
A
H
B
A
current
C
D
2.
3.
resistor 1
E
F
resistor 2
G
With the switch closed, use the voltmeter to measure the voltage drop between the
following points on the circuit. Note: Some readings will be zero!
a)
A to B
................ volts
b)
B to C
................ volts
c)
C to D
............... volts
d)
D to E
................ volts
e)
E to F
................ volts
f)
F to G
................ volts
g)
G to H
................ volts
h)
A to H
................ volts
i)
D to G
................ volts
j)
Ammeter
................milliamps
Looking at the measurement for a), c), e) and g), can you suggest how much energy is used
in the connecting wires?
...........................................................................................................................................
4.
How much energy is transferred by 1 coulomb of charge passing through Resistor 1?
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
5.
Reconnect the circuit with the Ammeter between the resistors. What do you notice about
the reading?
...........................................................................................................................................
Now disconnect the circuit and connect the voltmeter across the battery. The reading of the
voltmeter is a measure of the EMF (Electromotive Force) of the battery.
EMF of the battery is ............................
6.
What does this measurement say about how much energy is supplied to each coulomb by
the battery?
...........................................................................................................................................
7.
What can you say about the EMF and the total energy transferred in all the circuit
components?
...........................................................................................................................................
8.
Now sketch a graph in the space below of how the voltage changes in each section, A - B,
B - C, etc, as the current goes around the circuit, use your answers from Question 2.
Voltage Drop or Energy Loss
A
9.
B
C
D
E
F
G
H
Your answer to question 6 is how much energy the charge has as it leaves the battery.
Your answers to questions 2 and 8 show how much energy is lost in each section of the
circuit.
Now draw a graph of how much energy the charge has as it goes around the circuit, starting
with maximum at the beginnig and finishing with nothing by the end.
Energy level of Charge
A
B
C
D
E
F
G
Page 7
H
VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #2
CONVERTING
ELECTRICAL ENERGY INTO GRAVITATIONAL POTENTIAL ENERGY
PURPOSE
The purpose of this experiment is to first measure the energy supplied to a DC motor, then measure
the amount of energy converted into gravitational potential energy, and then finally determine the
efficiency of the conversion.
PARTNER
This prac will require two people.
EQUIPMENT
The equipment you will be using includes:• a power pack,
• voltmeter and ammeter,
• DC motor,
• set of slotted masses,
• frame with photogate,
• wires,
• mass holder.
•
•
•
electronic timer,
ruler,
electronic balance,
CIRCUIT
A
V
DC motor
Spindle
Mass holder with slotted mass in it
THEORY
The Electrical Energy produced can be obtained from the relationship:Energy = Power x Time (E = P.t )
The Power is given by
Power = Voltage Drop x Current ( P = V.I )
So the Electrical Energy supplied can be obtained from:
Electrical Energy = Voltage x Current x Time (E = V.I.t ),
where t is the time the mass holder takes to pass through the photogate.
This energy is used to raise the mass through the photogate. The gain in gravitational potential
energy required is :
Grav Potential Energy = Mass x Accel’n due to Gravity x Change in height ( E = mgh )
where h is the length of the mass holder.
Efficiency = Gravitational Potential Energy / Electrical Energy ( as a percentage)
PROCEDURE
The motor is clamped to the top of the frame with the mass holder initially on the floor. When the
motor is turned on, the holder will rise. You should turn off the power to the motor before the
holder reaches the motor because if it hits the motor, either the string will break, the masses will fly
off or the motor will be damaged.
If the mass rises too fast to measure either the voltage or the current, either lower the voltage or
increase the mass. Similarly if the mass does not move, increase the voltage or reduce the mass.
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VCE PHYSICS UNIT 1 - ELECTRICITY
JOBS
One person should turn on the power supply to the motor, read either the voltmeter or ammeter as
the mass holder goes through the photogate, and then turn the power off when the rising mass has
passed the photogate.
Another person should read both the other meter as the mass is rising.
The time for the mass holder to pass the photogate can be read afterwards.
MEASUREMENTS
Do the experiment for two different masses at two different voltages settings of the power supply.
Sample data in italics.
Length of mass holder (m)= .(0.12)...................... Supply Voltage Setting (V) = ....................
Set A
Mass (kg) = (0.3)
Set B
Mass (kg) =
Voltage (V) Current (A) Time (sec) Voltage (V) Current (A) Time (sec)
1
2
3
Average (3.5)
(0.60)
(0.65)
Length of mass holder (m) = ..........................
Supply Voltage Setting (V) = ......................
Set C
Mass (kg) =
Set D
Mass (kg) =
Voltage (V) Current (A) Time (sec) Voltage (V) Current (A) Time (sec)
1
2
3
Average
Sample Calculation: Elec Energy = 3.5 x 0.6 x 0.65 = 1.365 J, Grav PE = 0.3 x 9.8 x 0.12 = 0.353 J
Efficiency = Grav PE / Elec Energy = 0.353 / 1.365 = 26%
ANALYSIS
1.
For each of the four sets calculate the amount of electrical energy supplied.
Set A ....................................................................................................................................
Set B ....................................................................................................................................
Set C ....................................................................................................................................
Set D ....................................................................................................................................
2.
For each of the four sets calculate the amount of gravitational potential energy gained
Set A ....................................................................................................................................
Set B ....................................................................................................................................
Set C ....................................................................................................................................
Set D ....................................................................................................................................
3.
Calculate the efficiency of the motor for each set (Energy gained /Energy supplied)
Set A: ................................................
Set B: ................................................
Set C: ................................................
Set D: ................................................
4.
Comment on how the efficiency varies with mass and with voltage.
...........................................................................................................................................
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
VOLTAGE-CURRENT CHARACTERISTICS OF VARIOUS
ELECTRONIC COMPONENTS
Introduction
When a voltage is applied across a component, the amount of the current going through it
depends on its physical properties. How the current changes as the voltage is increased, also
depends on the particular component.
Some components even respond differently, depending on which end is connected to the positive
end of the battery.
In this next series of experiments you will be investigating the voltage-current characteristics of a
selection of components and how these components combine together.
NOTE: Later is this booklet is an experiment on Household Electricity Supply. There are three
sets of equipment - the Demonstration Model. So, at some time while you are doing the
experiments #5 to #9, you will be asked to do the experiment on the Household Electricty Supply
so that everyone will have a chance to work with one of the models.
EXPERIMENT #3
OHMIC RESISTOR
In this experiment you will be using a resistor, whose characteristics are similar to the metals that
make up wires and the heating elements in electrical appliances.
Equipment:
2 - 12V power supply
Switch
Milliammeter
Voltmeter
Resistor (one of larger resistors in the jar of components)
Construct the circuit below using a power supply. Record the current for voltages from 0 volts to 12
volt settings of the power supply.
Note that the voltage setings on the power supply only give a rough guide and the voltmeter should
be used to give a more accurate reading. Also, the current will be small, so use the milliamp scale.
switch
A
R
V
Voltage (V)
Current (mA)
Now plot the Voltage (Y - axis) against the Current in Amps on (X - axis) in the space over the
page, and draw a line of best fit through the origin.
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VCE PHYSICS UNIT 1 - ELECTRICITY
1.
The gradient of this line is called the Resistance. Calculate from your graph the resistance
of your resistor.
ohm
2.
Write down a relationship between Voltage, Current and Resistance.
...........................................................................................................................................
...........................................................................................................................................
3.
On your graph, draw a line you may get for a higher value resistance.
4.
The unit of resistance is the "ohm", what would be the equivalent unit in terms of volts and
amps?
1 Ohm = 1...............................
Plot your graph below
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #4
SERIES AND PARALLEL CIRCUITS
For any electrical conductor, a graph can be drawn showing the current flowing versus the voltage
across it.
In this experiment you will: plotting a voltage –current characteristics of two resistors on the one set of axes, then
 you will use the two graphs to predict the effective resistance if the two resistors were
combined in series, and finally
 measure the current and voltage for the combined resistors and seeing if your measurements
match your predicted graph.
And then repeat the last two steps for the two resistors connected in parallel.
Because you know that the resistors obey Ohm’s Law, you only need to take three sets of readings to
draw the voltage - current graphs for the resistors.
Equipment
2 - 12V power supply
Switch
Milliammeter
Voltmeter
Resistors (two different values from your jar, but ones that are reasonably close)
Procedure
1.
Set up a circuit to measure the voltage across and current through a resistor. Draw your circuit
below. ( See the previous experiment if you are not sure)
2.
Record 3 readings of Voltage and Current for each resistor ( R1 and R2).
Resistor 1
Voltage (V)
Current (mA)
Resistor 2
Voltage (V)
Current (mA)
3.
Graph the Voltage and Current values for both resistors on the one set of axes, putting the
Voltage on the Y-axis
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VCE PHYSICS UNIT 1 - ELECTRICITY
Plot your graph below
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VCE PHYSICS UNIT 1 - ELECTRICITY
series
R1
R2
In the Series Circuit, both conductors carry the same current.
This information can be used to predict the Voltage - Current graph for a Series connection.
4.
Construct your prediction of the line for the Voltage-Current relationship for the Series
Connection.
To do this, you use that fact that the current through each resistor is the same, but the total
voltage drop is just the sum of the individual voltages across each resistor.
To plot the line, first select a current and go up your graph until you hit each line. This gives
you the voltage drop across each resistor. Now add together these voltages and plot this value
further up with the current line you started with.
Do this with other current values. Now draw your line for the predicted Voltage- Current
relationship for the series connection.
5.
Now to test your prediction. Place the two resistors in Series in your circuit and measure a set
of Voltage and Current values.
Voltage (V)
Current (mA)
6.
Plot these results with a • on your previous graph.
7.
Do the experimental results agree with your prediction?
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
8.
Explain how you could use this method to find the effective resistance of three resistances in
series.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
parallel
R1
R2
In a Parallel Circuit, both resistors have the same voltage drop across them.
This information can be used to predict the Voltage - Current graph for a Parallel connection.
9.
Construct your prediction of the line for the Voltage-Current relationship for the Parallel
Connection.
To do this, you use that fact that the voltage drop across each is the same, but the current
coming in is just the sum of the individual currents going through each resistor.
To plot the line, first select a voltage and go across your graph until you hit each line. This
gives you the current in each resistor. Now add together these currents and plot this value
further across with the voltage line you started with. Do this with other voltage values. Now
draw your line for the predicted Voltage-Current relationship for the parallel connection.
10.
Now to test your prediction. Place the two resistors in Parallel in your circuit and measure a
set of Voltage and Current values.
Voltage (V)
Current (mA)
11.
Plot these results with an X on your previous graph.
12.
Do the experimental results agree with your prediction?
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #5
LIGHT GLOBE FILAMENT RESISTANCE
In this experiment, you will replace the resistor in the circuit from experiment #3 with a 12 V light
globe and remove the switch. Obtain the 12 volt globe from the trolley. Because the current drawn
by the light is larger, you will need to use the amp range of the ammeter.
Equipment
Your locker
The trolley
Power supply
Ammeter
12volt globe
Voltmeter
switch
Voltage (V)
Current (A)
This time graph the Voltage on the X - axis as it is the independent variable. That is, the voltage
and the properties of the component determine the size of the current.
Plot your graph below
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VCE PHYSICS UNIT 1 - ELECTRICITY
1.
Draw a smooth curve through your set of data. Describe the shape of your line.
..........................................................................................................................................
..........................................................................................................................................
2.
The resistance of the globe is given by the Voltage divided by the Current that it produces.
Calculate the resistance of the globe at voltages of 4, 8 and 12 volts.
R4V = ............
3.
R8V = ............
R12V = ............
Describe how the resistance of the globe changes as the voltage is increased?
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
4.
Give an explanation for your answers to Question 2 & 3.
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
5.
Is a light globe an Ohmic or Non-Ohmic device? Explain.
..........................................................................................................................................
..........................................................................................................................................
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #6
THE DIODE
The Diode is a Semiconductor component made of Silicon doped with Phosphorus and Aluminium.
It is an example of a device whose characteristics are not symmetrical, i.e. the size of the current
depends on which way the current is going through the component.
The diode only needs a small voltage to operate and it can handle only a small current, so the circuit
will need to be redesigned. Ensure that the power supply is set on 2 volts. To control the voltage or
potential drop across the diode, you will be using a variable resistor called a rheostat.. This allows
you to select the amount of voltage you want by sliding the contact from the left end to the right end.
Equipment
Your locker
The Trolley
Power supply set on 2 volts
switch
Diode
Voltmeter
Ammeter (milliamp scale)
Rheostat (the sliding contact of the rheostat corresponds to the arrowed connection
in the diagram below)
Rheostat
A
V
1.
Connect the circuit together and ask your teacher to check it before you press the switch.
Note that the diode has a band at one end, this corresponds to the line in the diagram above.
2.
Slowly adjust the control on the rheostat and measure several values of current and voltage.
Voltage (V)
Current (A)
3.
Turn the diode over so that the end with the band goes to the positive of the battery. Now
repeat step 2 above.
Voltage (V)
Current (A)
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VCE PHYSICS UNIT 1 - ELECTRICITY
4.
Graph both sets of results on the one set of axes. Draw the axes in the middle of the page.
Graph the data in step 3 as negative voltage and negative current, i.e. in the third quadrant.
Plot your graph below
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #7
LIGHT DEPENDENT RESISTOR (LDR)
The LDR is a semiconductor device whose resistance depends on the amount of light shining on it.
For a particular light intensity, the device obeys Ohm's Law over a small range of voltage.
In this experiment you will be investigating how the Resistance of the LDR varies as it is moved
closer to a light source, i.e. a light globe. The LDR is the small white device with the zig-zag lines
across the top. Use a 240 V globe from the trolley as the light source.
Use the circuit from Experiment #3, replacing the resistor with the LDR.
Equipment
Your locker
The trolley
1.
Power Supply
LDR
240 V light globe
Ammeter
Voltmeter
Place the LDR at about 50cm from the filament of the globe. Turn on the light, set the power
supply to a voltage to give a measure reading and record the voltage and current. Repeat this
for several values for the distance from the LDR to the light. Record your results in the table
below and calculate the resistance for each distance.
Distance to
Light
Voltage
(V)
Current
(mA)
Resistance
(ohm)
2.
In the space below plot a graph of Resistance versus Distance.
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VCE PHYSICS UNIT 1 - ELECTRICITY
4.
Describe the shape of the graph and suggest a relationship between the two quantities.
..........................................................................................................................................
..........................................................................................................................................
5.
If you wanted to check this relationship, what graph should you plot to achieve a straight
line.
..........................................................................................................................................
6.
Suggest an application for this device.
..........................................................................................................................................
..........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #8
THE THERMISTOR
The Thermistor is a semiconductor device whose resistance changes with Temperature. For a
particular temperature, the device obeys Ohm's Law over a small range of voltage. The Resistance
changes in an exponential way with Temperature, and as the Temperature falls, the Resistance rises.
In this experiment you will be calculating the Resistance from voltmeter and ammeter measurements
as the Thermistor cools down. You can then calculate the measure of your thermistor, which is the
“Perentage Change in Resistance for each degree centigrade”. The Thermistor will be placed in a
beaker of hot water and allowed to cool down over time.
Use the circuit from Experiment #3. The thermistor is on the trolley. It is the small black cylinder
about 2 cm long with red and black wires soldered to its ends.
Equipment
Front bench
The trolley
Your locker
1.
2.
Urn for hot water
Thermistor, small beaker, thermometer, stand, boss head and clamp
Voltmeter, ammeter, 6 V battery, switch and wires
Add hot water from the urn to a small beaker. Place the thermistor in the beaker. Put the
thermometer in the beaker and clamp it so that the bulb is at the same level as the thermistor.
Measure the temperature of the water, and close the switch to measure the Voltage and
Current readings. Now calculate the Resistance. Do this for several temperature values over
the next 10 minutes as the water cools down.
Temp
Voltage
Current
Resistance
3.
4.
Graph Resistance on tthe Y axis against Temperature on the X axis.
Describe the shape of the graph.
............................................................................................................................................
5.
Thermistors are compared by the percentage change in resistance for each degree centigrade.
To find this value for your thermistor, read from your graph two sets of resistance temperature values (R1, T1 and R2, T2).
The percentage change in the resistance (% change) = (R1 - R2) x 100 / R1.
The % change per degree centigrade is % change divided the temp difference, this equals
= % change / (T1 - T2). Calculate this value for your thermistor:
R1 : ......................., T1: ..........................., R2 : ......................., T2: ..............................
% change /degree Centigrade = ....................................................................................
.....................................................................................................................................
6.
Suggest an application for this device.: .........................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
EXPERIMENT #9
HOUSEHOLD ELECTRICITY SUPPLY
The Electrical Supply to households in Australia is set at 240 Volts AC, where AC stands for
Alternating Current. AC means that the current first goes one way through the circuit, then goes the
other way, then back again. This means the voltage at the terminals of the supply regularly reverses
direction. In Australia, the voltage does 50 complete cycles every second. That is, it has a frequency
of 50 Hertz (50 Hz).
The graph below of the voltage shows that it varies like a sine wave.
V +
0
0.01
0.02
time (sec)
-
A
+
A
lamp
N
0
N
0
Like a battery, AC needs two terminals. One is called the Neutral because it is kept at a voltage of 0
volts., while the other is called the Active because its voltage goes above and below the voltage of the
neutral wire.
The AC voltage in Australia is set at 240 volts. This value is not the maximum value or the peak
voltage as it is called. A more useful measure, since the electricity is used to run appliances, etc., is the
average voltage. This average is called the Root Mean Square value or RMS value for short.
So, the RMS value of the AC voltage is 240 volts.
The peak voltage is equal to 2 x RMS Voltage
1.
Calculate the Peak Voltage for AC voltage in your house.
...........................................................................................................................................
2.
...........................................................................................................................................
Indicate the Peak Voltage on the graph above.
The Wiring in a House Demonstration Board
Electricity enters the house by two wires, either from the power pole in the street, or from underground.
The two yellow terminals on the left of the board are the points where the electrical supply connects to
the house. The top terminal is the Active and the bottom terminal is the Neutral.
The two yellow wires first go into the Fuse Box.
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VCE PHYSICS UNIT 1 - ELECTRICITY
A.
3.
The Fuse Box
Unscrew the plastic screw at the bottom of the fuse box and look inside.
Where does the Active wire go to once it is inside the Fuse Box?
4.
...........................................................................................................................................
Can you suggest a reason for this?
...........................................................................................................................................
The Active wire now goes to each of the two Nilsen Federal fuses. Pull out one of the fuses
and locate the thin wire inside. This thin wire is made of a special metal which will melt when
the current reaches a certain level. The blue fuse is rated 16 amps and the brown fuse at 8
amps.
5.
Measure the resistance with a multimeter of the wire in the blue fuse in ohms
6.
...........................................................................................................................................
Calculate the energy loss, which produces heat, in the fuse when 16 amps is flowing through it
...........................................................................................................................................
7.
...........................................................................................................................................
A red wire now comes out of each fuse and goes into a three core cable.
What does the three core cable from the 16 amp fuse connect to? Why?
8.
...........................................................................................................................................
What does the three core cable from the 8 amp fuse connect to? Why?
...........................................................................................................................................
9.
Back to the Fuse Box
Where does the Neutral wire go to once it is inside the Fuse Box?
...........................................................................................................................................
This bar is called the Neutral Bar. There are several wires connected here. The green and
yellow wires are called the Earth wires. They are called this because the full green wire next to
them is connected to the Earth by being attached to the plumbing near the point where the water
pipe enters the house from the ground.
The black wires connected here are called the Neutral wires. They carry on the task of the
yellow neutral wire. That is, the current that comes out of a globe or switch passes through the
black neutral wire to the metal bar, and then out the yellow neutral wire back to the power pole.
Each three core cable has one red Active wire, one Black Neutral wire and one Green and
Yellow Earth wire.
Now replace the cover on the fuse box.
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VCE PHYSICS UNIT 1 - ELECTRICITY
B.
The Light and its switch
There are two red active wires leaving the fuse for the lights. These red wires are joined by
two black neutral wires from the Earth bar.
10.
Explain why the two lights are wired in parallel this way?
11.
...........................................................................................................................................
Draw a labelled diagram showing the active and neutral wires coming from fuse and the earth
bar, the two switches and the two globes.
C.
The Power Point
The power point consists of a switch and three slots for the plug from an appliance.
12.
Which wire in the three core cable is connected to the switch before connection to the power
point?
...........................................................................................................................................
13.
Draw a diagram of the switch and the three slots in the power point. Follow the wires from the
cable to the switch and the slots and label the slots Active, Neutral and Earth.
The power point on the right is assembled so that voltages between the wires can be measured.
Set the power supply to 6 volts and connect it to the yellow terminals.
14.
Turn on the switch to the right power point and measure the voltage across each pair of
terminals in the power point.
Voltage
Colours of Terminals
Measurement (V)
Between Active and Neutral
Between Active and Earth
Between Neutral and Earth
15.
Which two terminals give a reading of zero?
16.
...........................................................................................................................................
Give a reason for your answer to question 15.
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
D.
Preventing Electric Shocks
The Earth wire in the cable from the appliance, e.g. a toaster, is immediately attached to the
metal frame of the toaster on the inside. If any part of the toaster circuit breaks loose, then the
toaster will not function, but if this part of the circuit touches the metal case, then the case of
the toaster will be at 240 volts and could give a lethal electric shock even though the toaster is
not working. The attaching of the Earth wire to the metal case prevents this.
17.
Imagine that the active wire comes loose and touches the metal case. Describe the path of the
electricity from entering the house to leaving the house.
...........................................................................................................................................
...........................................................................................................................................
18.
...........................................................................................................................................
Comment on the overall resistance in this path and the effect on the size of the current.
...........................................................................................................................................
19.
...........................................................................................................................................
What will happen as a result of the effect on the size of the current?
...........................................................................................................................................
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VCE PHYSICS UNIT 1 - ELECTRICITY
Communication Article
Silicon Solar Cells Savour Sweet Sunshine of Success
Read the article. The information below explains some possibly unfamiliar words.
Glossary
Word
Paragraph
Fabrication
1
Irradiance
2
Current density 2
Spectral
3
Photons
3
Semiconductor
3
Amorphous
5
Obviate
6
Meaning
Making
Intensity of light measured in Watts per square metre.
Read as current.
Adjective from spectra
Particles of light
Material that is neither an insulator, nor a good conductor, e.g. Silicon
No shape, applied to materials, it means not a single crystal, but lots of
small crystals.
do without
From Robert Hill at Newcastle upon Tyne Polytechnic, UK
A new world record efficiency has recently been reported for silicon cells by Martin Green and
colleagues at the University of New South Wales, Australia (1989 Appl. Phys. Lett. 55, 1363). Such
devices convert sunlight directly into electrical power via the photovoltaic effect first observed by
Becquerel 150 years ago. The authors have been in the forefront of the revolution in silicon solar cell
design and fabrication over the past 10 years, and this recent paper records the achievement of cells
with an efficiency of 22.8 %. This record has since been surpassed by Green with a cell of 23.2 %
efficiency, reported at the recent European Photovoltaics Conference.
Under standard test conditions of 1 kW/m2 irradiance (similar to the Sahara Desert in summer at noon)
the output of Green’s cell is about 37 ma/cm2 at 0.63 V. i.e. 23.2 mW peak. The current density varies
linearly with irradiance, whilst the voltage has a logarithmic dependence, so the conversion efficiency
increases in concentrated sunlight. Efficiencies of close to 30 % have been achieved by three different
types of cell under sunlight concentrations of about 100 times standard condition.
Sunlight has a broad spectral range, whilst solar cells are most efficient for photons whose energy is
close to the semiconductor band gap. A better match to sunlight can be achieved by a number of
semiconductors each with a different band gap.
Such ‘stacked solar cells” using Gallium Arsenide/Gallium Antimonide have recently achieved a new
word record efficiency of 37 % in concentrated sunlight. Other combinations of semiconductors are
being tried, and efficiencies over 40 % are expected in the next 2 –3 years.
Mass-produced cells are inevitably less efficient and a 10 x 10 cm commercial cell would generate
about 3.5 A at 0.5 V under standard test conditions. Cells are usually used in modules, with 30 – 36
cells in series potted in a transparent rubber base with a glass front, metallised plastic back and an
aluminium surround for environmental protection and mechanical strength. Module efficiencies have
increased greatly, with a new world record 17 % efficient module announce recently by AEG. Both
AEG and BP Solar have already demonstrated 16 % efficient modules, which will be put in to
commercial production next year.
The cost of modules has decreased by a factor of about 6 over the past 10 years, to around $9 per watt
of peak output. New solar cell materials in the form of thin films semiconductors offer the potential of
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VCE PHYSICS UNIT 1 - ELECTRICITY
reducing this cost by a further factor of 5 –10. Amorphous silicon cells already power the ubiquitous
solar calculator and many other consumer products; about 10 MW of amorphous cells is produce each
year and output is set to double in 1990. Two other types of thin film cell are due to enter commercial
production, based on copper indium diselenide and cadmium telluride. Both of these materials have
demonstrated modules with efficiencies over 10 % and potentially longer lifetimes and low cost.
The market for solar vehicles and complete photovoltaic systems is growing rapidly – 35 MW in 1988
and all estimated 40 - 45 MW in 1989. Similar growth is set to continue for the foreseeable future.
Apart from consumer products, the main sales are for telecommunications, cathodic protection,
lighting, water pumping and vaccine refrigeration where tens of thousands of systems are performing
with high reliability and great cost-effectiveness. Even in the UK, it is now cheaper to light a garden
shed or telephone box with solar energy than run a mains cable more than 20 metres or so. Within the
next 20 years we should see many tens of megawatts of solar cells used in the UK, for instance
replacing the glazing of commercial buildings. Large scale power stations are already close to costeffectiveness in California for their peak load (due to air-conditioning) and a major future use could
well be in the electrolysis of water within a hydrogen based fuel economy to obviate the greenhouse
effect. Land usage of such stations in sunny climates is the same as that for coal or nuclear stations but
without their undesirable environmental impacts.
The three world records set in 1989 are significant technical achievements. Photovoltaics is no longer
just an enthusiastic dream: it is a significant international industry and is set to become a major
technology of the next century.
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VCE PHYSICS UNIT 1 - ELECTRICITY
Silicon Solar Cells Savour Sweet Sunshine of Success
Name:……………………………………
Questions
1.
What does the author mean by the “photovoltaic effect”?
………………………………………………………………………………….
………………………………………………………………………………….
2.
What are standard test conditions for solar cells?
3.
………………………………………………………………………………….
The Irradiance of 1 kWm-2 means that 1kilojoule of light energy passes through 1 square metre
every second. Estimate the area of the roof of the Science and Art Building and calculate how
many joules of energy would the roof receive in one hour on a sunny day.
………………………………………………………………………………….
4.
………………………………………………………………………………….
Using the information in Q’n 2, calculate the power input to a solar cell of area 1 sq cm from
light under standard conditions.
………………………………………………………………………………….
5.
………………………………………………………………………………….
The output of Green’s new cell is 37 mA cm-2 at 0.63 V. Use the relationship between power,
current and voltage to verify the output power stated in the article.
………………………………………………………………………………….
6.
………………………………………………………………………………….
The solar cell output in Question 5 is for 1.0 sq cm of solar cell. A solar photovoltaic plant
covers 2.5 km2. Calculate the total power output of the plant if it used Green’s new cell.
………………………………………………………………………………….
7.
………………………………………………………………………………….
Calculate the efficiency of the solar cell using your answers to questions 4 and 5.
………………………………………………………………………………….
8.
………………………………………………………………………………….
Using the data in paragraph 4 calculate the power output of a 10 x 10 cm commercial cell under
standard conditions.
………………………………………………………………………………….
9.
10.
11.
………………………………………………………………………………….
If a module is made up of 36 cells in series, what would be its power capacity?
………………………………………………………………………………….
Why are the cells arranged in series and not in parallel?
………………………………………………………………………………….
………………………………………………………………………………….
What is the cost of a 36 cell module?
………………………………………………………………………………….
12.
Each year producers make about 10 MW of amorphous cells. How many cells is this?
………………………………………………………………………………….
13.
Would electricity from a large solar power plant have greater, less or the same danger as
electricity from a coal fired power station? Explain
………………………………………………………………………………….
………………………………………………………………………………….
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VCE PHYSICS UNIT 1 - ELECTRICITY
1. Silicon Solar Cells savour sweet sunshine of success
1.
Name: Answers
Questions
1.
What does the author mean by the “photovoltaic effect”?
Electrical power from sunlight
2.
What are standard test conditions for solar cells?
1 kWm-2 irradiance.
3.
The Irradiance of 1 kWm-2 means that 1kilojoule of light energy passes through 1 square metre
every second. Estimate the area of the roof of the Science and Art Building and calculate how
many joules of energy would the roof receive in one hour on a sunny day.
Area = 30 x 150 m2. Energy = 1,000 x 30 x 150 x 60 x 60 = 1.6 x 1010 Joules
4.
Using the information in Q’n 2, calculate the power input to a solar cell of area 1 sq cm from
light under standard conditions.
1sq m = 100 x 100 sq cm, so input power = 1kW/10,000 = 0.1 Watt
5.
The output of Green’s new cell is 37 mA cm-2 at 0.63 V Use the relationship between power,
current and voltage to verify the output power stated in the article.
P = VI = 37 x 10-3 x 0.63 = 23 mW = 0.023 W
6.
The solar cell output in Question 5 is for 1.0 sq cm of solar cell. A solar photovoltaic plant
covers 2.5 km2. Calculate the total power output of the plant if it used Green’s new cell.
Output power = 0.023 x 2.5 x 1000 x 1000 x 100 x 100 = 58 x 107 W = 580 MW
7.
Calculate the efficiency of the solar cell using your answers to questions 4 and 5.
Efficiency = (0.023 / 0.1) x 100/1 = 23%
8.
Using the data in paragraph 4 calculate the power output of a 10 x 10 cm commercial cell
under standard conditions.
Power output = VI = 3.5 x 0.5 = 1.75 W
9.
If a module is made up of 36 cells in series, what would be its power capacity?
Power = 36 x 1.75 = 63 W
10.
Why are the cells arranged in series and not in parallel?
To produce a greater voltage, in parallel produces a larger current for a small voltage.
11.
What is the cost of a 36 cell module?
Cost = $9 per watt, each cell produces 63 W, so cost of module = 9 x 63 = $567
12.
Each year producers make about 10 MW of amorphous cells. How many cells is this?
Power output of cell = 1.75 W, so number of cells = 10 x 106 / 1.75 = 5.7 million.
13.
Would electricity from a large solar power plant have greater, less or the same danger as
electricity from a coal fired power station? Explain
Solar would have less environmental risk, the electrical risk, once the voltage is transformed to
higher voltages, would be the same.
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