This affiliate builds on the Gr vi and 7 electrical circuits work, and the previous chapter of this book. Up until at present, we have just been looking at uncomplicated circuits. Nosotros volition now examine the concept of series and parallel circuits. We will look at the difference betwixt these 2 set-ups in circuits, specifically looking at the effects of adding resistors in serial or in parallel and observing the alter in brightness of bulbs. The utilize of ammeters has too been included in this chapter. However, if yous exercise not have these instruments, you tin simply practise a qualitative study, using the brightness of the bulbs.
You tin also use the PhET simulations where learners can build their ain circuits and test them out, observing the effects when they add or remove various components. These simulations will run directly inside your browser from our website, world wide web.curious.org.za. Here is a link to a guide (in pdf format) written by PhET in the utilize of some of the electric excursion simulations: phet.colorado.edu/files/teachers-guide/circuit-structure-kit-dc-guide.pdf
three.1 Series circuits (ii.5 hours)
Tasks
Skills
Recommendation
Investigation: What happens when we add together more than resistors in series?
Investigating, hypothesising, following instructions, observing, interpreting, recording, analysing, writing, working in groups
CAPS suggested
Investigation: How does adding more cells in serial impact the current?
Investigating, hypothesising, following instructions, observing, interpreting, recording, analysing, writing, working in groups
Suggested
Investigation: Testing the current strength
Investigating, hypothesising, following instructions, observing, interpreting, recording, analysing, writing, working in groups
Suggested
3.ii Parallel circuits (3 hours)
Tasks
Skills
Recommendation
Action: Series or parallel?
Identifying, describing
Suggested
Investigation: How does adding resistors in parallel touch the current forcefulness?
Investigating, hypothesising, post-obit instructions, observing, interpreting, recording, analysing, writing, working in groups
CAPS suggested
Investigation: What happens to the current forcefulness when cells are connected in parallel?
Investigating, hypothesising, following instructions, observing, interpreting, recording, analysing, writing, working in groups
Suggested
Investigation: Testing the current force
Investigating, following instructions, observing, interpreting, recording, analysing, writing, working in groups
Suggested
Activeness: Which metals offer the most resistance?
Following instructions, observing, interpreting, working in groups
CAPS suggested
3.3 Other output devices (0.5 hours)
Tasks
Skills
Recommendation
Activity: Sankey diagrams
Cartoon, explaining
Suggested
Activity: History of electricity product
Research, summarising, working in groups, writing
CAPS suggested (tin exist washed every bit homework task)
Activity: Careers
Research, writing
Optional
Are there unlike types of electric circuits?
If all the light bulbs in a house are part of the same circuit, how can yous switch one lite off without the residue likewise turning off?
What is a series circuit?
What is a parallel excursion?
What happens when you connect more components in series or in parallel?
In the last affiliate, and in Gr 6 and 7, we take been looking at electrical circuits. These have mostly been series circuits. What does this hateful? And how else can a circuit exist arranged?
Series circuits
series
ammeter
ampere
resistance
A serial circuit is one in which there is only one pathway for the electrical current to follow. The components are arranged one subsequently another in a single pathway. When we connect the components we say that they are connected in series. We have already seen examples of series circuits in the last chapter.
A serial circuit with ane pathway for the current, from the negative to the positive terminal of the battery.
Ammeter
An ammeter is a measuring device used to measure out the electric current in the circuit. It is connected into the circuit in series. The electric current is measured in amperes (A).
The ampere is named after André-Marie Ampère (1775-1836), a French mathematician and physicist. He is considered the begetter of electrodynamics, which is the study of the issue of electromagnetic forces between electrical charges and currents.
An ammeter.
What is the symbol for an ammeter? Draw it hither.
Exercise yous think that an ammeter would take a high resistance or a low resistance to the current? Explain your choice.
Ammeters have an extremely low resistance considering they must not modify the current they are measuring in whatever way.
The ampere is often shortened to 'amp'.
A series circuit but provides one pathway for the electrons to follow. Let's investigate what happens when we increase the resistance in a series circuit.
What happens when we add more resistors in serial?
The aim of this investigation is to prove the learners that adding more than resistors in serial causes the overall resistance of the circuit to increase and that this reduces the current forcefulness.
AIM: To investigate the effect of adding resistors to a series circuit.
This is a good opportunity for grouping work if yous take enough equipment, but make certain that each learner is able to connect an ammeter correctly and is able to read the ammeter scale accurately. If y'all do not accept sufficient equipment for all the learners, y'all can do this experiment as a demonstration. Perhaps requite several learners an opportunity to come upwards to the forepart and help to connect the ammeters. If you lot practice non accept any ammeters then you can use the brightness of the bulbs to signal current forcefulness. The larger the current, the brighter the bulb volition glow. This ways that if the bulb glows brightly, it must accept a large electric current moving through information technology. If the bulb is dimmer, it means that there is a smaller current flowing through it.
If you do non have the physical apparatus for this investigation merely yous practise have net access, employ the PhET simulations establish here: http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc
The simulations are likewise useful considering the ammeters (and voltmeters) commonly used in schoolhouse laboratories are ofttimes not calibrated correctly or non serviced regularly and so often give slightly inaccurate results.
HYPOTHESIS: Write a hypothesis for this investigation.
This is a learner-dependent reply. The hypothesis should relate the dependent and independent variables and make a prediction. The dependent variable volition modify as the contained variable is changed. Here is an instance of a possible answer:
As the number of resistors increases, the current strength decreases.
MATERIALS AND APPARATUS:
1,5 5 cells
3 torch bulbs
insulated copper conducting wires
switch
ammeter
Information technology is important that the torch bulbs have the same resistance and are not randomly selected. The switch is non an essential role of this investigation. Information technology can exist left out of the circuit.
METHOD:
Construct the circuit with the cell, the ammeter, 1 bulb and the switch in series.
A photo showing the setup.
Close the switch, or the circuit if you lot are not using a switch.
Note how brightly the bulb is shining and write down the ammeter reading. Draw a excursion diagram.
Circuit ane
Add together another light seedling into the circuit.
Note how brightly the bulbs are shining and write downward the ammeter reading. Draw a circuit diagram.
Circuit ii.
Add the tertiary light bulb into the circuit.
Notation how brightly the bulbs are shining and write down the ammeter reading. Depict a circuit diagram for the last excursion you built.
Circuit iii.
RESULTS:
Complete the table:
Number of bulbs in series
Brightness of bulbs
Reading on ammeter (A)
1
ii
iii
The brightness of the bulbs is a qualitative comparison. Learners should utilise "vivid, brighter, brightest" as a mode to draw the glowing bulbs. The graph should show the quantitative information of the ammeter reading and the number of bulbs. If you practice not take an ammeter to have readings, either do not depict a graph, or alter the graph to a bar graph which has vivid, brighter, brightest as the values on the y-axis. This is not a particularly useful graph but will give the learners a chance to practise cartoon a bar graph and give them a visual representation of the decrease in current strength as the number of bulbs increases.
Depict a graph to testify the human relationship between the number of bulbs and the current.
These results are an example of possible results. The actual results obtained by the learners volition differ but the tendency should be similar. Every bit the number of bulbs in series increases, both the ammeter reading and bulb brightness should subtract.
Number of bulbs in series
Brightness of bulbs
Reading on ammeter (A)
1
brightest
0,xv
2
bright
0,07
3
dimmest
0,05
Using standard ammeters may not requite perfect results and if the bulbs are immune to oestrus up too much in between adding more than bulbs, their resistance will exist higher. It is of import that the learners see a downward trend.
Analysis:
What happened to the brightness of the bulbs equally the number of bulbs increased?
The bulbs got dimmer as more than bulbs were added.
When you had two bulbs, did they glow with the same brightness, or was one brighter than the other?
The bulbs glowed with the same brightness.
When you had 3 bulbs, did they glow the same as each other or was one brighter than the others?
The bulbs glowed with the same brightness.
What exercise your answers to the previous questions tell you about the current in the series circuit?
If all the bulbs glow the aforementioned, information technology ways that they all experience the same current. This means that the current is the same everywhere in a series circuit.
What happened to the reading on the ammeter as y'all added more bulbs in series?
The ammeter reading decreased.
CONCLUSION:
Based on your answers, what happened to the current when more bulbs were added in series?
As more bulbs were added, the current decreased.
Is your hypothesis accepted or rejected?
This answer will depend on the hypothesis written by the learner at the start of the investigation.
As more resistors are added in series, the full resistance of the circuit increases. Equally the total resistance increases, the electric current strength decreases. What would happen if nosotros increased the number of cells connected in series? Would the current become larger or smaller? Let's investigate.
How does adding more cells in serial affect the current?
This investigation will show that calculation more cells in series increases the current strength. Be careful with this activity considering if you exercise not have enough resistance in your circuit, you can damage the torch light bulbs. Apply at least two torch low-cal bulbs or a torch calorie-free seedling and a resistor in order to continue the resistance high enough. If you take ammeters, you can use quantitative data to show that adding more cells in series increases the electric current force. If you exercise non take ammeters, then use the brightness of the bulbs as qualitative data. Use terms such as dim, bright, brightest. The learners will non be able to draw effective graphs with the qualitative data but yous could give them the example data in the teacher's guide and inquire them to draw a line graph if they demand practice.
AIM: To investigate the issue of increasing the number of cells connected in series on the electric current strength.
HYPOTHESIS: Write a hypothesis for this investigation. Remember to mention how the increment in the number of cells will impact the electric current strength.
This reply is learner-dependant. They must mention how the dependent variable volition be afflicted past the independent variable. Remember that the hypothesis does non need to exist factually correct. They will prove or disprove it by completing the investigation. Hither is an instance of a possible hypothesis: Every bit the number of cells continued in series increases, the current strength increases.
MATERIALS AND APPARATUS
three i,5 V cells
insulated copper conducting wires
ammeter
ii torch light bulbs (or ane torch light bulb and i resistor)
METHOD:
Construct a excursion with 1 cell, the ammeter and the two torch light bulbs.
Observe the brightness of the bulbs and tape the ammeter reading in the table of results. Draw a excursion diagram.
Circuit i.
Add a second cell in serial and notice the brightness of the bulbs. Describe a circuit diagram of your circuit.
Record the ammeter reading in the table of results. Draw a circuit diagram.
Circuit 2.
Add together a tertiary prison cell in series and detect the brightness of the bulbs. Describe a excursion diagram of your excursion.
Tape the ammeter reading in the tabular array of results. Draw a circuit diagram.
Circuit three.
RESULTS:
Complete the table:
Number of cells in series
Brightness of bulbs
Reading on a mmeter (A)
1
ii
3
These results are example results. The actual results obtained by the learners will differ simply the trend should exist similar. Equally the number of cells increases, both the ammeter reading and the bulb brightness should increase.
Number of cells in serial
Effulgence of bulbs
Reading on ammeter (A)
one
dimmest
0.07
2
vivid
0.15
3
brightest
0.22
Determination:
What tin you conclude from the shape of the graph?
As the number of cells continued in series increases, so does the current forcefulness.
Is your hypothesis true or fake?
This answer depends on the learner'due south original hypothesis.
We have seen that increasing the number of cells in series increases the current, but increasing the number of resistors decreases the current.
We will now investigate the current strength at different points in a series excursion.
Testing the current strength
The first investigation looked at the decrease in electric current strength when more resistors were continued in series. This investigation confirms that the current forcefulness is the same at all points in a series excursion. This is an optional investigation. This tin exist a demonstration if your equipment is limited. This is a good opportunity for grouping work, only make sure that each learner is able to connect an ammeter correctly and understands the ammeter scale.
INVESTIGATIVE QUESTION:Is the current forcefulness the aforementioned at all points in a serial circuit?
HYPOTHESIS: Write a hypothesis for this investigation. What practice you lot call up volition happen in this investigation?
This is a learner-dependant reply. Learners need to mention the independent and dependent variables. The dependent variable will modify as the contained variable is changed.
Here are two examples of an acceptable hypothesis:
The electric current will be different at different points in the circuit OR
The current volition be the same at different points in the circuit.
MATERIALS AND APPARATUS:
insulated copper connecting wires.
2 ane,5V cells
ii torch light bulbs
ammeter
METHOD:
Set up a series circuit with two cells and ii torch light bulbs in series with each other.
Insert an ammeter in serial between the positive final of the battery and the first torch seedling.
Measure the current strength using the ammeter. Draw a circuit diagram of this set up.
Excursion ane.
Remove the ammeter and close the circuit again.
Insert the ammeter in series betwixt the two torch bulbs.
Mensurate the current strength using the ammeter. Draw a excursion diagram of this set.
Circuit 2.
Remove the ammeter and close the circuit again.
Insert the ammeter in series between the terminal torch seedling and the negative terminal of the batteries.
Mensurate the current strength using the ammeter. Draw a excursion diagram of this set up.
Circuit iii.
RESULTS:
Complete the following table:
Position of ammeter in circuit
Ammeter reading (A)
Between positive final of prison cell and first bulb
Between two bulbs
Betwixt negative terminal of cell and last bulb
The ammeter readings should be the same at any bespeak in the series circuit.
CONCLUSIONS:
Write a conclusion based on your results.
The current strength is the same at any point in a series circuit.
Is your hypothesis true or simulated?
This respond will depend on the hypothesis written past the learner at the start of the investigation.
In a serial circuit, there is only one pathway for the electrons to move through. The current forcefulness is the same everywhere in that pathway.
What take we learned about serial circuits?
There is only one pathway for the electrons to follow.
The current flows at thesamestrengtheverywhere in a series excursion, considering at that place is only i pathway. We say that the current is the aforementioned at all points in the circuit.
If y'all add together more resistors in series, the electric current in the whole circuit decreases.
Why does the electric current stay the same at all points? Allow's recollect about how electric current moves through a circuit. Practice you lot remember that we spoke virtually the delocalised electrons in metals in the last chapter?
The electrons in a usher normally drift in various dissimilar directions inside a metal, every bit shown in the diagram.
Delocalised electrons move freely in a conducting wire.When the wire is connected in a closed circuit, the electrons move towards the positive terminal of the bombardment.
When we build a airtight excursion with a jail cell every bit an energy source, the electrons will all begin to motion towards the positive side of the prison cell. The rate at which the electrons motion, is determined by the resistance of the conductor.
There are electrons everywhere in the conducting wires and electrical components. When the circuit is closed, all the electrons start moving in the same general direction at the aforementioned time. This is why a calorie-free bulb turns on immediately when you shut the switch.
[link]
The simulation identified in the visit box helps to demonstrate how a low-cal bulb turns on immediately when the switch is turned on.
In a serial circuit, all the electrons travel through every component and wire as they travel through the circuit. All the electrons experience the same resistance and so they all move at the same charge per unit.
This means that in the diagram below, the readings on all iii ammeters will be the same, so: A1= Aii= Aiii
Parallel circuits
parallel circuit
Parallel circuits offering more than one pathway for the electrons to follow. When constructing a parallel excursion, we say that components are connected in parallel.
Look at the diagram which shows how ii light bulbs are connected in parallel.
At that place are two paths for the current in this parallel excursion, one path through each of the bulbs.
How tin y'all tell whether or not a circuit is connected in series or in parallel? Let's look at some circuit diagrams to tell the difference.
Picket a video that explains the departure between series and parallel circuits
Series or parallel?
INSTRUCTIONS:
Look at the following circuits and determine which are in series and which are in parallel. The serial circuits will only offer one pathway, but the parallel circuits will have more than 1 pathway for the electrons to follow.
serial
parallel
parallel
series
Let's investigate how parallel circuits work.
How does calculation resistors in parallel affect the current strength?
This investigation will show the learners that increasing the number of resistors in parallel to each other, causes the overall resistance of the circuit to decrease and the current strength to increment. There is no need to talk over how to summate the effective resistance of a parallel circuit. The learners just demand a qualitative agreement.
AIM: To investigate the effect of calculation resistors in parallel on the current strength.
HYPOTHESIS: Write a hypothesis for this investigation.
This is a learner dependant answer. Learners need to mention the contained and dependent variables. The dependent variable will change as the independent variable is changed.
Here are two examples of an acceptable hypothesis:
Equally more bulbs are added in parallel, the electric current force will decrease OR
Every bit more bulbs are added in parallel, the current force will increase.
MATERIALS AND APPARATUS:
one,5 5 prison cell
three identical torch bulbs
insulated copper conducting wires
switch
ammeter
Information technology is important that the torch bulbs are the same resistance and not randomly selected. The switch and ammeter are not strictly necessary for this experiment. They can exist left out if you don't accept plenty switches or ammeters.
METHOD:
Construct the circuit with the cell, ammeter, one bulb and the switch in series.
Annotation how brightly the bulb is shining and record the ammeter reading. Draw a diagram of your circuit.
Add another calorie-free bulb, in parallel to the showtime, into the circuit.
Note how brightly the bulbs are shining and record the ammeter reading.
Add together the 3rd light bulb, in parallel to the kickoff two, into the circuit.
Annotation how brightly the bulbs are shining and record the ammeter reading.
RESULTS:
Complete the table:
The brightness of the bulbs is a qualitative description. The learners should utilise "brilliant, brighter, brightest" in gild to describe the glowing bulbs.
Number of bulbs in parallel
Brightness of bulbs
Reading on ammeter (A)
1
two
3
Depict a graph to show the relationship between the number of bulbs and the current.
The graph will show the relationship betwixt the main electric current (reading on the ammeter) and the number of bulbs connected in parallel. Every bit more bulbs are connected in parallel, the current strength should increase because the overall resistance of the excursion decreases. This means that the graph should be a directly line with an increasing tendency. Standard ammeters may not exist accurate enough to produce a perfectly straight line. This is not every bit important as seeing the upward trend.
These results are just an example. The actual results will depend on the circuit ready by the learner.
Number of bulbs in parallel
Brightness of bulbs
Reading on ammeter (A)
1
dimmest
0.xv
2
brighter
0.3
3
brightest
0.45
Analysis:
What happened to the brightness of the bulbs equally the number of bulbs increased?
The bulbs got brighter as more than bulbs were added.
When you had two bulbs, did they glow with the same effulgence or was one brighter than the other?
The bulbs glowed with the same effulgence.
When y'all had three bulbs, did they glow the same brightness or was one brighter than the others?
The bulbs glowed with the same brightness.
What exercise your answers to the previous questions tell you nearly the electric current in the parallel branches of the circuit?
As all the bulbs are identical, if they all glow the same brightness, and so they all feel the aforementioned current. This means that the electric current is the same in each branch.
What happened to the reading on the ammeter as you lot added more bulbs in parallel?
The ammeter reading increased.
CONCLUSION:
Based on your answers, what happened to the current when more bulbs were added in parallel?
As more bulbs were added, the current increased.
Is your hypothesis truthful or false?
This answer will depend on the hypothesis written by the learner at the offset of the investigation.
As more than resistors are added in parallel, the total current strength increases. The overall resistance of the circuit must therefore have decreased. The current in each light bulb was the same because all the bulbs glowed with the aforementioned brightness. This tells us that the electric current of electrons must have split upward and moved through each of the branches.
We tin can also connect cells in parallel. What would happen if we increased the number of cells connected in parallel? Would the electric current get stronger or weaker?
What happens to the current strength when cells are connected in parallel?
AIM: To investigate how increasing the number of cells connected in parallel affects the current strength in a circuit.
HYPOTHESIS: Write a hypothesis for this investigation.
This is a learner-dependent answer. Learners need to identify the independent and dependent variables. The dependent variable will modify as the independent variable is changed.
Hither are two examples of an adequate hypothesis:
As more than cells are added in parallel, the electric current strength will decrease OR
Equally more than cells are added in parallel, the current strength will increase.
MATERIALS AND APPARATUS
three 1,5V cells
one torch light bulb
insulated copper conducting wires
ammeter
The ammeter is not essential to the experiment. The brightness of the bulb can serve as a qualitative measure out.
METHOD:
Set up a excursion which has ane jail cell, the ammeter and the torch light bulb in series with each other. Draw a circuit diagram of your excursion.
Discover the brightness of the bulb and record the ammeter reading.
Connect another jail cell in parallel with the first cell. To connect the second cell in parallel, connect a wire from the positive terminal of the get-go cell to the positive terminal of the second cell. Connect some other wire between the negative terminal of the first bombardment and the negative terminal of the 2d battery. Draw a excursion diagram of your circuit.
Discover the brightness of the seedling and tape the ammeter reading.
Connect a tertiary jail cell in parallel to the other two cells. Draw a circuit diagram of your circuit.
Find the effulgence of the bulb and tape the ammeter reading.
RESULTS:
Consummate the table:
The brightness of the bulbs is a qualitative clarification. The learners should use "bright, brighter, brightest" in gild to describe the glowing bulbs. The ammeter readings should stay the aforementioned.
Number of cells in parallel
Brightness of seedling
Reading on ammeter (A)
1
2
three
CONCLUSION:
What did yous notice nigh the brightness of the bulbs?
The brightness of the bulbs should not change.
What did yous notice nearly the ammeter readings?
The ammeter readings are the same.
What conclusion can you draw from your results?
Adding cells in parallel does non modify the overall current strength.
Adding cells in parallel has no overall consequence on the current forcefulness. The current strength stays the aforementioned if you add cells in parallel.
We saw that the electric current strength increased when bulbs were continued in parallel. However, we were only testing the electric current forcefulness at ane point in the parallel circuit. How does the electric current compare in the different pathways of the circuit? Let's exercise an investigation to find out.
Testing the electric current strength
The beginning investigation looked at the increase in current strength when more than resistors were connected in parallel. This investigation confirms that the current strength is not the aforementioned at all points in a parallel excursion. This is a good opportunity for group work, only make certain that each learner is able to connect and read an ammeter correctly. If you exercise not have enough equipment to allow for small groups to build the circuits, you can rather use this investigation as a demonstration. Perhaps give several learners an opportunity to come upwards to the forepart and assistance to connect the ammeters.
INVESTIGATIVE QUESTION: Is the current force equal at all points in a parallel circuit?
MATERIALS AND Apparatus:
insulated copper connecting wires.
two one,5V cells
three identical torch light bulbs
ammeter
METHOD:
Set upwards a parallel circuit with ii cells in series with each other and three torch calorie-free bulbs in parallel with each other.
Insert an ammeter in serial between the cells and the first pathway, every bit shown in the diagram.
Mensurate the current force using the ammeter.
Remove the ammeter and close the circuit again.
Insert the ammeter in series in the first pathway.
Mensurate the current strength using the ammeter.
Remove the ammeter and shut the circuit again.
Insert the ammeter in series in the second pathway.
Measure the current forcefulness using the ammeter.
Remove the ammeter and close the circuit again.
Insert the ammeter, in series, in the third pathway.
Measure out the current forcefulness using the ammeter.
Remove the ammeter and close the excursion again.
Insert the ammeter in series betwixt the first pathway and the cells on the reverse side to the first reading.
Measure the electric current force using the ammeter.
RESULTS:
Position of ammeter in circuit
Ammeter reading (A)
betwixt the prison cell and first pathway
in the first pathway
in the 2d pathway
in the tertiary pathway
between the cell and the start pathway
These are some example readings to show the trend:
Position of ammeter in circuit
Ammeter reading (A)
betwixt jail cell and first pathway
0.9
in the kickoff pathway
0.iii
in the second pathway
0.iii
in the 3rd pathway
0.3
between the cell and the first pathway
0.9
If you practice non use identical bulbs, then the readings in each of the branches will not be identical, but they will add up to reading in the main branch. If possible, it is worthwhile to demonstrate this to learners.
CONCLUSION:
Write a determination based on your results.
The current strength is non the aforementioned at all points in a parallel circuit. If the bulbs are identical, then the current is the aforementioned in the three branches, withal the current in the main role of the circuit is greater than that in the individual pathways. The current in the primary part of the excursion is the sum of the currents in the pathways.
Is your hypothesis true or false?
This reply will depend on the hypothesis written by the learner at the start of the investigation.
What accept we learned about parallel circuits?
At that place is more than i pathway for the current to follow.
The current divides between the different branches so that each branch gets some of the current. As the torch bulbs in each branch in our example were identical, the current divided equally between them.
If you add together more resistors in parallel, the total electric current supplied past the cell in the excursion increases.
Why does the current divide when offered an alternative pathway?
Imagine that you lot are sitting in a school hall during assembly. You are bored and waiting for it to terminate then that you can become out to break to chat to your friends. There is only one leave from the hall. When you are dismissed, everyone has to exit through the same door. It takes a while considering only some learners tin leave at a time.
Now imagine that there is a second door that is the aforementioned every bit the first door. Now you and your friends accept a choice of which door to go through. The speed at which the learners exit the hall will increase and some of you will get out through the first door while others will exit through the second door. No i can get through both doors at the same time.
This is similar to the way current behaves when in a parallel circuit. As the electrons approach the branch in the excursion, some electrons volition take the start path and others volition take the other path. The current is divided between the two pathways.
In the post-obit circuit A1 = A4 and A1 = A2 + A3 and A4 = A2 + A3
We have looked at how resistors and cells behave in series and parallel circuits. Allow'due south wait at how different metals conduct electricity. All conductors take some resistance in a excursion. Are some metals meliorate conductors of electricity than others?
Let'south have a expect at which metals offer more resistance than others to the flow of charge (electric current) through an electric excursion .
Which metals offer the about resistance?
This activity only compares the effect of the type of material on resistance. The other factors that affect resistance volition be covered in the Grade nine Energy and Change syllabus.
Each metal will take a particular resistance based on the resistivity. You lot do not need to measure the resistance of each metallic, all that is required is a qualitative clarification of the light bulb. The brighter the light seedling, the higher the electric current. If there is a loftier current information technology means that there is little resistance. So the brighter the bulb glows, the less resistance offered by the metallic wire. The learners may brand small mistakes if the brightness of the bulbs is hard to distinguish.
Utilise whichever metallic wires you lot have bachelor. Effort to get copper and nickel. You lot could twist aluminium foil into a wire (just brand sure it is the same length and approximate thickness as the other metals). Aluminium wire will frequently ignite if placed in a circuit and then test it beforehand and make sure that it does not get too hot. If you lot utilize the materials listed beneath, then nichrome will have the highest resistance, followed past zinc, and so aluminium and copper has the lowest resistance of the 4.
MATERIALS:
a cell
torch light bulb
insulated copper wires
lengths of copper, aluminium, zinc and nichrome wire
crocodile clips (if available)
The actual length of wire that you use is not important, but they should all be the same length and thickness. If you cannot detect these metals, any other combination of metals tin can be successfully used.
INSTRUCTIONS
Build a circuit with the cell and the torch light bulb and leave a gap for the metal to exist tested. You lot can employ crocodile clips at the end of each slice of metallic for easy insertion.
Insert each metal into the circuit (one at a time).
An case circuit with a jail cell, a light bulb and the slice of metal existence tested.[link]
Observe the brightness of the seedling.
QUESTIONS:
Describe a circuit diagram of your apparatus.
An example circuit diagram with the break in the circuit where metals are to exist tested shown on the left.
Why tin can we employ the brightness of the bulb to qualitatively mensurate resistance?
Loftier resistance opposes the movement of electrons, decreasing the current so there is less energy for the light bulb. The higher resistance wire will cause the seedling to be dimmer than the lower resistance wire.
List the metals in social club of increasing resistance.
Copper, aluminium, zinc and nichrome.
Why do you think copper is used for connecting wires in electric circuits?
Copper has an extremely low resistance, and then has a minimal effect on the overall resistance of the circuit. Other materials would add to the overall resistance of the circuit, decreasing the maximum possible current in that circuit.
There are several factors which influence the amount of resistance a textile offers to an electric electric current. We accept seen that the blazon of fabric is 1 of those factors.
In Gr 9 we will expect at the other factors that influence resistance. If y'all desire to run into the content in other grades, recall that you lot can visit world wide web.curious.org.za
Other output devices
Light bulbs are not the simply devices used in electrical circuits. Devices that use electrical energy to role, including light bulbs, are chosen output devices. Let'southward look at some other common examples of output devices.
LEDs (Light-Emitting Diodes)
LEDs are widely used electronic devices. They are small lights but they practice not have a filament similar an incandescent bulb has. They therefore cannot burn down out, as there is no filament to wearable out, and they do not get as hot. LEDs are used in electronic timepieces, high definition televisions and many other applications. Larger LEDs are besides replacing traditional light bulbs in many homes because they practise not use as much electricity. They last longer than incandescent bulbs and are more efficient.
Sentinel this video about the history of the LED
Unlike LED bulbs.
In the last chapter, we looked at the energy transfers in an electrical organization. We will now represent energy transfer within electric systems in a different way. We will apply this new representation to the difference between energy outputs in an LED and an incandescent lite seedling.
Video on drawing a basic Sankey diagram.
Sankey diagrams
Sankey diagrams were first introduced in the Gr seven CAPS workbook as a style of representing the transfers of energy inside a organisation, specifically focusing on the transfer of input energy to useful and wasted output energy. They provide a very clear illustration of the process. This links back to the previous chapter to reinforce learning.
You might accept drawn Sankey diagrams in Grade vii. If non, here is some quick revision.
In an energy system, input energy is transferred to useful output energy and wasted output energy. A Sankey diagram is a visual and proportional representation of the energy transfers that happen in a system.
For instance, a kettle uses about 2000 J of input energy, merely only about 1400 J is used to rut the water. The remaining 600 J is wasted as sound. Hither is the Sankey diagram to represent the free energy transfer.
Remember that energy is measured in joules (J).
QUESTIONS:
We will now compare an LED with an incandescent light seedling.
Depict a Sankey diagram for an LED if the input energy is 100 J, 75 J of energy is used to produce light and the rest is lost as heat.
Depict a Sankey diagram for a filament light bulb if the input energy is 100 J, the wasted heat energy is lxxx J and the rest produces low-cal.
Which seedling exercise you recall is more than efficient? Explain your answer.
The LED bulb is more efficient as more of the input energy is transferred to useful output (light) than is wasted as estrus. In the filament light bulb, much more free energy is wasted every bit heat.
Can y'all recollect of any other output devices? Make a list of equally many every bit you tin can.
Some are: motors, buzzers, beepers.
History of electricity production
INSTRUCTIONS:
Work in groups of three or iv.
Enquiry the history of electricity production: How was electricity discovered and how did electricity become widely used?
Create a basic timeline for the discovery of electricity and it'southward production.
The timeline does not demand to be too specific. We desire learners to realise that this was not an overnight discovery, but involved many people over a pregnant time. Here are some pertinent facts. This listing is not consummate and not all of the dates are necessary. Another useful resource is available here: http://www.timetoast.com/timelines/118814
600 BC - Discovery that bister, rubbed with silk, would attract calorie-free objects such every bit feathers
1600 AD - William Gerbert coined the term electricity. He was the get-go to make a link between magnetism and electricity
1700s - Wimshurst car, used to generate static electricity
1752 - Benjamin Franklin proved that lightning was a form of electricity
1800s - Sir Humphrey Davey discovered electrolysis; Volta created the showtime simple cell
1831 - Michael Faraday demonstrated electromagnetic induction
1825 - Ampere published his theories on electricity and magnetism. The unit of current, the ampere, is named afterward him
1827 - George Ohm published his report of electricity. The unit of resistance, the ohm, is named after him
1831 - Charles Wheatstone and William Fothergill created the telegraph machine
1870 - Thomas Edison congenital a DC generator
1876 - Alexander Graham Bell invented the telephone which uses electricity to transfer oral communication
1878 - Joseph Swan demonstrated an electric lite seedling
1880s - Nikola Tesla developed an Ac generator
1881 - The commencement British public electricity generator was built in Surrey
1883 - Magnus Volk built the first electric train line
1896 - Nikola Tesla established hydroelectric power plants in America
1905 - Albert Einstein demonstrated the photoelectric effect which led to the production of photovoltaic cells
Careers
INSTRUCTIONS:
Choose a career related to electricity product.
Write a short paragraph describing the career. Include data on how ane can report or prepare for your chosen career.
The Eskom website has data regarding various careers and the internet has many different sources.
A series circuit has only one pathway for the electrons to travel through.
A parallel circuit has more 1 pathway for the electrons to travel through.
In a series circuit, the current is the same at all points in the circuit.
In a series circuit, the resistance increases as more resistors are added in series.
In a parallel circuit, the electric current splits between the available paths.
In a parallel excursion, the resistance decreases as more resistors are added in parallel.
Revision questions
Await at the following circuit diagrams and decide whether they are series circuits or parallel circuits. Write the correct respond in the space below each diagram. [six marks]
Serial
Parallel
Series
Parallel
Series
Parallel
Look at the three circuit diagrams. Rank the circuits from brightest bulb to dimmest bulbs. [3 marks]
Explain your choices in the previous question. [5 marks]
The first excursion has the brightest bulb considering it has the to the lowest degree resistance and so information technology has the highest electric current. The tertiary circuit has the highest resistance because it has two resistors continued in series with the lite bulb. The more resistors connected in series, the higher the resistance and the lower the current.
Await at the iii circuit diagrams. Rank the circuits from brightest bulb(due south) to dimmest bulb(s). [three marks]
Dimmest, vivid, brightest
Explicate your choices in the previous question. [five marks]
The third circuit will accept the brightest bulb because adding resistors in parallel lowers the overall resistance in the excursion. The electric current is therefore greater and the bulb shines brighter. The outset circuit is the dimmest because it has no parallel branches, and and so offers the highest resistance.
Look at the circuit diagram below. Each lite seedling is identical.
Is this a series or parallel circuit? Explain your reply. [two marking]
How do the brightness of bulbs A, B and C compare? (which is the brightest?) [3 marks]
What would happen to the brightness of the bulbs if the switch was opened? Explain your reply. [5 marks]
This excursion has both series components (the cell and bulb A are in serial) and a parallel co-operative consisting of seedling B and C.
Bulb A is the brightest, Bulbs B and C would have the aforementioned effulgence as each other.
If switch S is opened, and so bulb C will not glow. Bulbs A and B would at present have equal brightness merely they would be dimmer than when the switch was closed. A and B would now exist in series with each other and at that place is no parallel co-operative. The overall resistance of the circuit would therefore exist higher, resulting in a smaller current.
Report the following diagram.
What is the human relationship between the ammeter readings on A1 and A4? In other words, how exercise the current strengths compare at these points in the excursion? Explain your reply. [3 marks]
What is the human relationship between the ammeter readings on A1, A2 and A3? In other words, how do the current strengths compare at these points in the circuit? Explain your answer. [three marks]
A1 = A4. The total current flows through the excursion at both of these points.
A1 = A2 + A3. The current splits between parallel branches in a circuit.
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