CASTLE Unit 2-READING 1

Transcription

1 Schematic Diagram Figures CASTLE Unit 2-EADING 1 Up to this point in our study of electricity, we have been representing our circuits by drawing real life pictures of the circuit components. As we begin to study more complicated circuits it is necessary to introduce a simple, standard design for circuit components. These specialized symbols are recognized internationally by scientists and engineers. When using these specialized symbols, we call the circuit picture a schematic diagram, sometimes referred to as a circuit diagram. When drawing schematic diagrams the convention is to replace cells, batteries, bulbs, etc which may be made by different companies, have different covers (Energizer vs. Duracell) or shapes and sizes (like bulbs) with a single symbol for ANY cell, bulb, wire, etc What follows is a list of EAL PICTUES and their SCHEMATIC SYMBOLS which are to be used in schematic diagrams. Your job is to learn the proper symbols for each. Consider the example of a complete circuit below. eal Picture Schematic Diagram + _ Diagrammatic Symbols On the next page you will find a list of common circuit components and their schematic equivalent. Modeling Workshop Project C2 EAD 1 v3.1

2 Name eal Picture Symbol Single cell + - Battery (three cells) ** note a battery is a combination of cells. You can make a battery with as many cells as you want just keep adding single cells together! ound Bulb (not lit) ound Bulbs (Lit) ** Note any kind of rays emanating from the bulb are good enough to indicate the bulb is lit + - Long Bulbs (Not Lit) L Long Bulbs (Lit) L Capacitor Compass (deflecting clockwise) Compass (deflecting counterclockwise) Modeling Workshop Project C2 EAD 1 v3.1

3 What is a capacitor? Two layers of conducting material separated by a layer of an insulator form what is called a CAPACITO. The name comes from the capacity of this three-layer device to store both charge and energy. The conducting layers are called PLATES. The insulating layer is sometimes referred to as a dielectric layer. The insulating layer prevents movement of charge from one plate to the other inside the capacitor. You can make a simple capacitor by placing a sheet of waxed paper between two sheets of aluminum foil. In most capacitors the plates have very large surface area, so that they can store a large amount of charge. The plates are also made very thin, so that the three layers can be rolled into a cylinder and placed inside a small can. Each plate has a screw or a wire attached to it, called a TEMINAL, which extends outside the can and allows the plate to be connected to a circuit. The charge-holding ability of a capacitor is called its CAPACITANCE. Capacitance is measured in a unit called the FAAD, named after the British scientist Sir Michael Faraday ( ). The blue capacitor in your CASTLE kit has a capacitance of farad, or 25,000 micro-farads, µf. (Some kits may also have a small silver capacitor, which will not be used at this time.) Your teacher will have some large silver capacitors, which are to be shared by the class in a number of activities. These have a capacitance of 0.1 farad, or 100,000µF four times as much as the blue capacitor. NOTE: Sometimes capacitor plates may pick up stray charge that needs to be removed. A good way to avoid this problem is to keep a wire connected to the terminals of your capacitor when you are not using it. Also, after using a capacitor you will want to reset it so you can start all over again. To do this, touch a wire simultaneously to both of the capacitor terminals. Modeling Workshop Project C2 EAD 1 v3.1

4 Name CASTLE Unit 2 - Activity 1 Date Pd Circuit A Circuit B Connect circuit A. Carefully disconnect one wire and insert the battery as shown in circuit B. Call your instructor over to watch you connect Circuit B. To repeat the process, be sure and ESET the capacitor before completing Circuit A. Prediction(s): Circuit Set-up Will the bulbs light? What is the effect of a capacitor on a closed loop? Observation(s): Circuit Set-up Did the bulbs light? Circuit A Yes / No Circuit A Yes / No Circuit B Yes / No Circuit B Yes / No On the back of this page, describe your explanations for both predictions. Use the terms and models that were developed in Unit 1. Underline the physics terms you use. Conclusion: Consensus: New Terms: Modeling Workshop Project 4 1 C2 ACT 1 v3.2

5 Circuit Will the bulb light? 1 Charging 1 A B D Prediction(s) 2 2 Name CASTLE Unit 2 - Activity 2 C You should use the blue capacitor. You will use the compass to test the wires labeled A G shown in the schematic diagrams. emember to rotate the circuit while keeping the compass in one place! Where does the mobile charge originate during the charging and discharging process? E Date Discharging 1 Circuit F G 2 Observation(s) Pd Did the bulb light? 1 2 charging Y / N Y / N discharging Y / N Y / N Circuit Point Compass Deflection? A CW CCW NO B CW CCW NO C CW CCW NO D CW CCW NO E CW CCW NO F CW CCW NO G CW CCW NO Conclusion: CW Clockwise CCW Counterclockwise NO No Deflection Use your observations to answer the focus question! Conclusion: charging Y / N Y / N discharging Y / N Y / N Circuit Point Compass Deflection? A CW CCW NO B CW CCW NO C CW CCW NO D CW CCW NO E CW CCW NO F CW CCW NO G CW CCW NO New Terms: Modeling Workshop Project C2 ACT 2 v3.1

6 Name CASTLE Unit 2: Activity 3 How does a Genecon behave like a battery? Date Pd Procedure: Turn the handle of the Genecon in a direction and speed so that the direction of charge flow and bulb brightness are the same as a 1-cell, 2-cell, and 3-cell battery. Count the number of turns of the handle that you make in 10 s for each trial. epeat three times for 1-cell, for 2-cells and for 3- cells. Prediction(s): How will the brightness of the bulbs in the 1-cell circuit compare to the 2- cell and 3-cell circuits? How does a Genecon behave like a battery? Number of Cells 1-cell Observation(s): Bulb Brightness Compass deflection. How will the compass deflection for the 1-cell circuit compare to the 2- cell and 3-cell circuits? How will the number of turns of the Genecon handle to match the bulb brightness in the 1-cell circuit compare to the number turns to match the 2-cell and 3-cell circuits? 2-cell 3-cell Number of Cells 1 cell 2 cell Number of turns for each trials 1 st 2 nd 3 rd Avg 3 cell Conclusion: Consensus: Modeling Workshop Project C2 ACT 3 v3.1

7 CASTLE Unit 2: eading 2 Electrical Energy The term energy is probably one you often use. However, if you attempt to define it, you may find it difficult to do so. Energy is the ability to make something happen. We have identified a number of things that happen in circuits charges move, compasses deflect, bulbs heat and give off light. What is the source of the energy that makes these things happen? In most of the circuits we have observed, the source of the energy has been the battery. In some circuits, however, there was no battery present. When a capacitor discharges, it can make these same things happen, so it must also have been a source of energy, at least temporarily. In some circuits, a Genecon was used, but the source of energy was the energy stored in your muscles. The cranking action transformed the energy from muscle storage to the energy of moving charges and bulbs releasing light. You know that batteries eventually wear down, and may become dead. This means that they no longer have sufficient energy stored in them to make something happen in a circuit. Some batteries are called rechargeable and can be re-used. This is an incorrect term, however, since the batteries task was never to supply charge to the circuit it was already there! These batteries would more properly called re-energizeable. In the circuit, charge originates in every conductor, and constantly re-cycles around the circuit. However, energy leaves the energy source and travels one-way, leaving the circuit as heat thermal and light energy radiating from the bulbs (the receivers of the energy). The energy source might be the stored chemical energy in a battery, or the stored energy in muscles used to crank a Genecon, the stored electrical energy in a charged capacitor. Modeling Workshop Project C2 ead 2 v3.1

8 Stored Energy and echargeable Batteries A fresh battery (such as a single D-cell) generally contains two substances, which we will refer to as A and B. These are high-energy substances (like some foods are known to be excellent sources of energy), which means that energy is stored in the chemical bonds within these substances. These two chemicals react inside the battery cell and release the energy that pushes charges around the circuit. The reaction is rolling down the energy hill when energy is released from the cell. The equation for the reaction is: A + B C + D + energy Eventually, however, substances A and B will be used up completely converted into low-energy substances C and D. When only substances C + D are left, we refer to the battery as dead. Some batteries, however, are designed so that the chemical reaction is reversible. By pumping energy back into the system from another source, the chemical reaction can be forced in the opposite direction. The diagram on the right below demonstrates energy being absorbed into the battery, climbing the energy hill. The equation for the reaction is: Energy + C + D A + B The battery is now refreshed or reenergized and can be used again to pump charges around a circuit. (The term rechargeable is misleading, since a battery never runs out of charge. Charge is present everywhere in the circuit, and is not supplied by the battery. The battery simply supplies the energy needed to make the charge move through the circuit. The term re-energizable battery would be more accurate.) Modeling Workshop Project C2 ead 2 v3.1

9 Name CASTLE Unit 2 - Worksheet 1 Capacitors and Charge Flow Date Pd Bulbs A and B light temporarily when the circuit in Figure 1 below is connected. A B Figure 1 B Figure 2: Will A and B light? A 1. Will bulbs A and B light when connected as shown in figure 2? Explain your answer in detail. Using a battery, bulbs, wires, and a capacitor explain how: 2. to charge a capacitor 3. to discharge a capacitor 4. to find out if a capacitor is already charged without discharging it. Modeling Workshop Project C2 WS 1 v3.1

10 Below are sketches of possible patterns of charge flow during the interval when the capacitor is charging, and when it is discharging. For each sketch, state whether or not the charge flow shown is correct (circle your answer). Support your answer by stating what is wrong with the charge flow arrows or what is correct about them. Use evidence to support your explanation. 5. Charging 6. Discharging + _ A) Correct Incorrect B) Explanation: A) Correct Incorrect B) Explanation: 7. Charging 8. Discharging + _ A) Correct Incorrect B) Explanation: A) Correct Incorrect B) Explanation: Modeling Workshop Project C2 WS 1 v3.1

11 Name Date Pd CASTLE Unit 2: Activity 4 The Air Capacitor Focus Question: How does an air capacitor operate? Section of drinking straw Near end Near End Far end Far End Procedure: Perform the task described in the left column. Fill in each space provided in the chart. Answer the focus question in your conclusion. Procedure Describe total amount of air in both chambers of the air capacitor Describe movement of air in both chambers of the air capacitor Near Chamber Far Chamber Near Chamber Far Chamber While blowing into near end with the far end open Increasing Decreasing emaining Constant Moving in Moving out No movement While blowing into near end with the far end covered (closed) by your finger. After blowing into near end with the far end open, closing the far end (w/ finger) then opening both ends Conclusion: Consensus: Modeling Workshop Project C2 ACT 4 v3.1

12 First sketch in the corresponding electrical circuit in the space provided. Then answer the following Focus Question by filling in the missing blanks in the chart below. The Air Circuit Corresponding Electrical Circuit (Sketch the circuit in the space below.) Near End Far Air moves this way Focus Question: How is the air circuit analogous to an electrical circuit? Air Circuit Electrical Circuit The air pump causes air to move around the loop. Pinching the tube so that it is completely closed off. The air that enters the near chamber is not the same air that comes out of the far chamber. The air in the tubes, chambers, and pump that is already present before any action is taken. When charge stops moving, the positive(top) plate of the capacitor has an excess of charge. After charging has stopped, the negative (bottom) plate has a deficiency of charge. The insulator between the plates. Conclusion: Consensus: Modeling Workshop Project C2 ACT 4 v3.1

13 CASTLE Unit 2 - eading 3 Benjamin Franklin s + and - notation Movable charge is normally present in all conducting matter. Adding some charge to a normal capacitor plate will result in there being more than the normal amount of charge in the plate, while removing some charge will result in there being less than the normal amount of charge in the plate. Benjamin Franklin ( ) came to the same conclusions when he did his pioneering work in electricity a few years before the American evolution. Franklin is the person who first used (+) and (-) symbols in electricity. He used them to represent these two conditions: (+) represents a MOE-THAN-NOMAL amount of charge ( extra charge) (-) represents a LESS-THAN-NOMAL amount of charge ( missing charge) In the next section we shall begin using these symbols with the same meanings Franklin gave them. Franklin never knew about two kinds of charge. During the nineteenth century, the evidence for two kinds of charge became more compelling. Franklin s symbols were retained but later given different meanings as excesses of one kind of charge or the other. In this curriculum, the evidence for two kinds of charge will be presented in Section 8. Modeling Workshop Project C2 ead 3 v3.1

14 Name Date Pd CASTLE Unit 2 - Worksheet 2 Answer the following questions based on the air capacitor activity. Explain your reasoning in detail. 1. Does any of the air blown into one side of the capacitor come out the other? Explain. 2. How can you recognize a neutralized air capacitor? Explain. 3. For the air capacitor model, explain what happens when air is forced into one side of the capacitor. 4. In the air capacitor model, explain what happens when air was drawn out of one side of the capacitor. 5. What are the similarities between the purposes of the membrane and the air capacitor and the insulating layer in the electric capacitor? Modeling Workshop Project C2 WS 2 v3.1

15 6. What are the physical differences between the insulator in the circuit capacitor and the membrane in the air capacitor? 7. Sketch a qualitative graph that represents the amount of air in the near chamber vs. time during the charging of the air capacitor. Sketch on the same set of axes a qualitative graph for the far chamber of the air capacitor. Use the following types of lines to represent each of the chamber volumes: near: far : Chamber Volume normal volume time Modeling Workshop Project C2 WS 2 v3.1

16 Name CASTLE Unit 2 - Activity 5 Date Pd Capacitor charging. Prediction(s) How will the bulb lighting time during charging of the blue capacitor compare to the bulb lighting time during charging of the silver capacitor? (greater than, less than or equal to) What effect does the size of a capacitor have on the amount of charge and energy stored in the capacitor? Capacitor discharging. Observation(s) You should perform multiple trials of both charging and discharging and record average values in the space below. Variable Bulb lighting time during charging. Blue Capacitor How will the number of turns of the genecon crank hand during discharging of the blue capacitor compare to the number of turns during discharging the silver capacitor? Number of turn of the Genecon handle during discharging Variable Bulb lighting time during charging. Silver Capacitor. Number of turn of the Genecon handle during discharging Conclusion: Consensus: Modeling Workshop Project _C2 ACT 5.doc v3.2