Download Science 9 - Rocky View Schools

Science 943 - Electrical Circuits
Text Reference

Science Focus 9 pp. 272 to 278
Learner Outcomes
Students will:
Describe technologies for transfer and control of electrical energy

use switches and resistors to control electrical flow, and predict the effects of these and other
devices in given applications

describe, using models, the nature of electrical current; and explain the relationship among
current, resistance and voltage

measure voltages and amperages in circuits, and calculate resistance using Ohm’s law

develop, test and troubleshoot circuit designs for a variety of specific purposes, based on low
voltage circuits
Background Information
Electric circuits provide a continuous pathway for charges to move.
1. Complete the following.
(a) Define electricity
(b) Complete the following system diagram.
Input
Process
Output
(c) Define an electrical circuit.
Science 943 Circuit Diagrams
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(d) Use the following diagram to identify and describe the key components in a circuit.
Circuit Elements and Diagrams
Even the most complex electrical circuits are made up of only four basic elements or
components.

Source: the source of electrical energy (usually a battery)
Conductor: the wire through which current flows

Load: items along the circuit that convert electrical energy into other forms of energy

Control: a switch or device that can turn the circuit or devices along it on or off.
Nearly everyone who designs and works with electrical circuits uses symbols and circuit
diagrams. You have been provided with an illustration of the component. Complete the
rest of the chart by (a) describing the component, and (b) drawing a sketch of the symbol
used to represent the component. The last one has been done for you because it was not
on this web page.

Component
Science 943 Circuit Diagrams
Description of the Component
Draw a Sketch of the Symbol
Used to Represent the
Component.
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To control electricity flowing in
a circuit it is sometimes
necessary to reduce the current.
To do this we use resistors and
the amount of resistance is
shown on the resistor by a
number of coloured bands.
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Drawing a Circuit Diagram
Your circuit diagram should meet the following components.

Draw with a pencil and ruler on graph paper or unlined
paper.

Place components in a rectangle or square arrangement.

Make conductors straight lines with right-angled
corners.

If possible, arrange your diagram so conductors do not
cross.

Draw neatly, making symbols a consistent size.
Closed circuit
In order to light a light bulb (lamp), a circuit must be closed.
1. Go to the OHM zone web site. (http://www.article19.com/shockwave/oz.htm). This is
an interactive web site that allows you to build your own circuits by dragging and
dropping different components into the circuit board.
2. Make a circuit that has one battery, a switch, a light, and conductors connecting these
components together.
3. Click on the “Visualize” button (the goggles) to see if your circuit is closed. If it is,
you will “see” the current flowing through the circuit. If it is an open circuit, you will not
“see” the current flowing through the circuit.
4. Use the rules above to draw a circuit diagram of the circuit that you just made.
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Measuring Electric Current
Ampere - unit of flow
Electric current is the amount of charge that passes a point in a conducting wire every
second.
The term ampere (A) is the unit of electric current flow. The symbol for current is “I”
The greater the amount of electric flow or current that is being conducted through a wire
the greater the amperage. For example, a current flow of 2-Amps is flowing twice as fast
as a flow of 1-Amp. A current flow of 4-Amps is flowing four times faster than a flow of
1-Amp.
G
A galvanometer is an instrument used to measure a very weak electric current. The
is the symbol for a galvanometer in a circuit diagram.
An ammeter is an instrument used to measure a stronger electric current. The
is the symbol for an ammeter in a circuit diagram.
A
Measuring Voltage
The amount of work required to move a charge between two points, or the work per unit
charge, is called the electric potential difference between the two points. The unit used
to measure electric potential is called the volt or voltage (V).
The instrument for measuring voltage is called a voltmeter.
V
The
is the symbol that is used to show a voltmeter in
circuit diagram.
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1. Go to the OHM zone web site. (http://www.article19.com/shockwave/oz.htm). This is
an interactive web site that allows you to build your own circuits by dragging and
dropping different components into the circuit board.
2. Make a circuit that has one battery, a switch, a light,
and conductors connecting these components together.
Close the switch.
2
3
3. Add an ammeter to the system in the locations shown
on the chart below and record the electric current passing
through the circuit. The first one has been done for you.
1
Location of Ammeter
1
Amperes of current
flowing through the
circuit at that point
(A)
0.9996
2
3
4. Add a second light bulb to the electric circuit and record the electric current passing
though the circuit.
Location of Ammeter
1
Amperes of current
flowing through the
circuit at that point
(A)
0.4999
2
3
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1. Go to the OHM zone web site. (http://www.article19.com/shockwave/oz.htm). This is
an interactive web site that allows you to build your own circuits by dragging and
dropping different components into the circuit board.
3
1
2
2. Make a circuit that has one battery, a switch, a light,
and conductors connecting these components together.
Close the switch.
3. Add a voltmeter to the system in the locations shown
on the chart below and record the electric current passing
through the circuit. The first one has been done for you.
Location of Voltmeter
1 – across the battery
2 – across the light bulb
3 – across any two points in
the circuit
Potential Difference Or
Voltage
(V)
10
4. Add a second light bulb to the electric circuit and record the electric current passing
though the circuit.
Location of Voltmeter
1 – across the battery
2 – across the light bulb
3 – across the second light
bulb
4 – across any two points in
the circuit
Potential Difference Or
Voltage
(V)
10
If one thinks of an electrical circuit in analogy to water circulating in a network of pipes,
driven by pumps in the absence of gravity, then the potential difference corresponds to
the pressure difference between two points. If there is a pressure difference between two
points, then water flowing from the first point to the second will be able to do work, such
as driving a water wheel.
You are now done your worksheet!
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