Unit D Lesson 9: Circuits
Completion requirements
Unit D Lesson 9: Circuits
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Learning Targets |
Big Question: What are the details on circuits?
Like streets and avenues in a city, circuits can be designed in many different ways, depending on what you need them to do.
Like streets and avenues in a city, circuits can be designed in many different ways, depending on what you need them to do.
At the end of this inquiry, you should be able to answer the following questions:
- What is the difference between a series circuit and a parallel circuit?
- Which parts of a house are wired in series and which are in parallel?
- What is a schematic diagram?
- What is the function of a transistor?
- What are the components of a microcircuit?
Pages 311 and 315 in your textbook will help you answer these questions.
Background Information
The Need For Schematics
To build a house, people need to use various plans. Some of those plans tell the framers where the walls go. Others tell the plumbers where to put the pipes. Electrical diagrams, called schematic diagrams, are used to guide the installation of electrical components.
Engineers, electricians, and scientists are some of the occupations that use schematic diagrams. A schematic diagram is turning an actual drawing into a symbolic drawing using standard symbols.
To build a house, people need to use various plans. Some of those plans tell the framers where the walls go. Others tell the plumbers where to put the pipes. Electrical diagrams, called schematic diagrams, are used to guide the installation of electrical components.
Schematic diagrams for an electric circuit show the four basic parts of every circuit: switches, loads (resistors), conductors, and sources.
Figure 1 β Home plans can involve several schematic diagrams like this one.
A Schematic Example
If you had to draw all the items of an electric circuit as real-life representations, doing the drawings could take a long time. For example, imagine a simple circuit with a battery, bulb, and switch. Drawing the wires would probably be easy, but how do you draw a bulb, a switch, or a battery? Even if you are a good drawer, what you draw might look totally different than what someone else draws. That's why using symbols is a much better solution for drawing circuits.
In the example to the right (Figure 2), the real-life representation of the circuit is on top, but on the bottom is the much simpler schematic diagram. You can see how schematics are simpler and can save a lot of time as well.
If you had to draw all the items of an electric circuit as real-life representations, doing the drawings could take a long time. For example, imagine a simple circuit with a battery, bulb, and switch. Drawing the wires would probably be easy, but how do you draw a bulb, a switch, or a battery? Even if you are a good drawer, what you draw might look totally different than what someone else draws. That's why using symbols is a much better solution for drawing circuits.
In the example to the right (Figure 2), the real-life representation of the circuit is on top, but on the bottom is the much simpler schematic diagram. You can see how schematics are simpler and can save a lot of time as well.
What do the Schematic Symbols Mean?
Figure 3 to the right is a universal chart indicating most of the common electrical symbols that you need to know for Grade 9 Science.
Refer to page 312 in Science in Action 9 for a detailed list. Refer to pages 509 and 510 for additional information for identifying electrical symbols.
Figure 3 to the right is a universal chart indicating most of the common electrical symbols that you need to know for Grade 9 Science.
Refer to page 312 in Science in Action 9 for a detailed list. Refer to pages 509 and 510 for additional information for identifying electrical symbols.
Figure 3 β This chart represents just some of the most common schematic symbols.
Watch
You need not to be an artist to draw electric circuits, but schematic drawings must be concise. The following videos will help you to understand the process of producing schematic drawings.
For a lesson on drawing simple circuits, watch the following video, "How to Draw Simple Electric Circuits Lesson".
For a lesson on drawing simple circuits, watch the following video, "How to Draw Simple Electric Circuits Lesson".
How do you hook a voltmeter and an ammeter into a circuit properly? Watch the following video "Drawing Electric Circuits with Voltmeter and Ammeters" to learn how.
Types of Circuits
When you watched the videos and examined schematic diagrams, you may have noticed patterns in the drawings of the various circuits. That occurs because all circuits are categorized into two types: parallel circuits and series circuits. Both have advantages and disadvantages.
When you watched the videos and examined schematic diagrams, you may have noticed patterns in the drawings of the various circuits. That occurs because all circuits are categorized into two types: parallel circuits and series circuits. Both have advantages and disadvantages.
Series Circuit
Imagine if all the circuits in your house were connected in series. When the switch was closed, all the lights and all other electrical devices would be on. You could not switch off your room light without turning off all the lights and devices β hugely inconvenient!
However, houses have all circuits connected in series to a main power switch so that the power for the entire house can be turned off if such is needed in an emergency.
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Series circuits have only one path for electrons.
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You can see from this image that all the current travels in one path.
- If one light bulb burns out, then no electrons can pass to the second light bulb, both bulbs will not light up.
Imagine if all the circuits in your house were connected in series. When the switch was closed, all the lights and all other electrical devices would be on. You could not switch off your room light without turning off all the lights and devices β hugely inconvenient!
However, houses have all circuits connected in series to a main power switch so that the power for the entire house can be turned off if such is needed in an emergency.
Parallel Circuits
Having your house wired in parallel means you are able to operate items such as the toaster without having to turn on every electrical device in the house. Fuses and/or circuit breakers are very important in case too much current is drawn. The fuse will burn out or the breaker will trip and fire from overheated wires generally is avoided.
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Parallel circuits are the type of circuits you see in homes β the electrons have more than one pathway.
- If the bulb on one of the pathways burns out, the other bulb will still light because electricity can flow into the bulb on the alternative pathway and back to the battery.
Having your house wired in parallel means you are able to operate items such as the toaster without having to turn on every electrical device in the house. Fuses and/or circuit breakers are very important in case too much current is drawn. The fuse will burn out or the breaker will trip and fire from overheated wires generally is avoided.
What are the advantages and disadvantages of a
series circuit
?
Advantages
Disadvantages
All the lights (loads) can be controlled with one switch.
If the wire is cut or the switch is turned off, all devices are shut off. Each device cannot be run separately.
Adding devices increases the resistance of the entire circuit and, therefore, the current will decrease, which might make the bulbs dimmer.
Adding devices increases the resistance of the entire circuit and, therefore, the current will decrease, which might make the bulbs dimmer.
What are the advantages and disadvantages of a
parallel circuit
?
Advantages
Disadvantages
Each device has its own path to the current source (such as a battery). Therefore, the circuits can operate individually.
Another advantage to a parallel circuit is that when you add new pathways, you do not affect the resistance in the circuit and therefore do not affect current. If you add more light bulbs, they still shine as bright as if it were one bulb in the circuit.
Another advantage to a parallel circuit is that when you add new pathways, you do not affect the resistance in the circuit and therefore do not affect current. If you add more light bulbs, they still shine as bright as if it were one bulb in the circuit.
Because less resistance means more current available to the circuit, increasing the number (or size) of devices means increasing the current. This could be a potential fire hazard if the current becomes too high. (That's why breakers are protection!)
More energy is used because each device uses its maximum voltage.
More energy is used because each device uses its maximum voltage.
Watch
Parallel circuits to the rescue! Watch the video "Types of Electrical
Circuits" to find out why parallel circuits serve a great purpose in your home.
Want to get serious about series and parallel circuits? Watch the video "Series and Parallel Circuits".
Why do all the lights on a Christmas tree go out when one light burns out? Watch the video "Electrical Circuits" to find out.
Practice Activity
Practice Worksheet: Circuit Simulation
- DOWNLOAD this practice worksheet (S9_UD_S2_L9_circuit_sim). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
- Click here
to visit the simulation website. Simply drag the bulbs, wires, and batteries you wish to use from the upper left corner into the simulation work space. Connect items with wires by bringing the ends close together. Disconnect them by moving
the end of a wire away from the item. Experiment, and have fun! While you are experimenting, answer the questions on the worksheet.
- When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
1a.
b. By having a complete circuit with no breaks in the wires, the light bulb will stay turned on. Electricity is the constant flow of electrons.
2a.
b. The bulbs are connected in series, which means only one pathway is available for the current to travel.
c. Old-style Christmas lights on a tree (if one bulb goes out, the rest go out β these types of light strings are actually becoming very rare, modern Christmas light strings will continue to function if one bulb goes out)
3a.
b. The current has other pathways to go through to complete the circuit.
c. In a house where one room can have a light on and the others can be off.
4. A series circuit β less cost due to less wiring needed. Also, the battery would last longer.
5. A parallel circuit so maximum voltage is available to all electronic loads. Circuits can be operated independently of one another.
6a.
b. By having a complete circuit with no breaks in the wires, the light bulb will stay turned on. Electricity is the constant flow of electrons.
2a.
b. The bulbs are connected in series, which means only one pathway is available for the current to travel.
c. Old-style Christmas lights on a tree (if one bulb goes out, the rest go out β these types of light strings are actually becoming very rare, modern Christmas light strings will continue to function if one bulb goes out)
3a.
b. The current has other pathways to go through to complete the circuit.
c. In a house where one room can have a light on and the others can be off.
4. A series circuit β less cost due to less wiring needed. Also, the battery would last longer.
5. A parallel circuit so maximum voltage is available to all electronic loads. Circuits can be operated independently of one another.
6a.
- Add more voltage
- Decrease resistance
- Add more resistors in a series circuit
- Decrease the voltage
- Insert too much voltage
- Have too many pathways for the current in a parallel circuit with too much voltage
Connections
Connections β Technology
>> Microcircuits
The circuits in cars, houses, and other buildings use complex organization of many circuits. However, circuits are also essential in small environments such as inside a computer. Computers use microcircuits (integrated circuits), which are tiny circuits. The microcircuits cannot fit the mechanical style of switches, so transistors are used. A transistor is a 3-layer piece of silicon that acts as a switch in a microcircuit.
Did you know the first microcircuit in the form of a microchip was developed in 1961? Early microcircuits were used in Air Force computer systems and to make portable calculators. These microchips consisted of one transistor, three resistors, and one capacitor; they were the size of your small finger.
Todayβs microchips are in many electric devices such as computers, cell phones, and microwaves. Microchips today contain more than 125 million transistors in a space smaller than a penny β which sounds more like bacteria than real stuff.
>> Microcircuits
The circuits in cars, houses, and other buildings use complex organization of many circuits. However, circuits are also essential in small environments such as inside a computer. Computers use microcircuits (integrated circuits), which are tiny circuits. The microcircuits cannot fit the mechanical style of switches, so transistors are used. A transistor is a 3-layer piece of silicon that acts as a switch in a microcircuit.
Did you know the first microcircuit in the form of a microchip was developed in 1961? Early microcircuits were used in Air Force computer systems and to make portable calculators. These microchips consisted of one transistor, three resistors, and one capacitor; they were the size of your small finger.
Todayβs microchips are in many electric devices such as computers, cell phones, and microwaves. Microchips today contain more than 125 million transistors in a space smaller than a penny β which sounds more like bacteria than real stuff.
Figure 4 β Transistors are a very common part of modern circuits.
Watch
Did you know many people use microchips on a daily basis? To learn more about microcircuits, watch the video "Computer Basics: How does a
microchip work".
Did you know your cell phone 100 000 000 transistors? To learn more about the exciting world of microcircuits, watch the video "How Does a
Transistor Work".