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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 page 1 (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. page 2 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. Science 943 Circuit Diagrams page 3 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. Science 943 Circuit Diagrams page 4 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. Science 943 Circuit Diagrams page 5 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 Science 943 Circuit Diagrams page 6 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! Science 943 Circuit Diagrams page 7