Electrical Experiments. Circuits, Electromagnets, and Motors

Transcription

1 Electrical Experiments Circuits, Electromagnets, and Motors Student Project for ENGR 3030 Service Learning Engineering Design Western Michigan University Spring 2005 Semester Jenna Hiller, Andrew Rockwell, and James Spencer Faculty Advisor: Dr. Andrew Kline Revision, further testing, and editing in Spring 2006 by Paula Lupina, American Humanics Intern Classroom tested in April, 2005 Additional Testing in February and March, 2006 at the Kalamazoo Area Boys and Girls Club 1

2 Activity 1: Circuit Board Useful Terms for Circuit Board Activity: Voltage: Current: Amperage: Terminal: Circuit: Resistor: Series: Parallel: potential difference across an object measured in volts flow of electric charge the rate of flow of a current of electricity expressed in amperes a device attached to the end of a wire or cable or to electrical equipment for making connections the complete path of an electric current any object that resist the movement of electrical charge an arrangement of the parts of or elements in an electric circuit whereby the whole current passes through each part or element without branching an arrangement of electrical devices in a circuit in which the same potential difference is applied to two or more branches Brief comments: Within the figures the red line represents a connecting wire with an alligator clip at each end and a yellow circle indicates that the bulb should be lit. The figures and explanation position wires to specific bulbs, different bulb can be used as long as the same pattern is used. Supplies: Provided circuit board and accessories Figure 1: Circuit Board Setup Student Activity Sheet Circuit Board 1

3 Figure 2. Take one connecting wire and attach it to the (positive) +terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on the Bulb 2 mount. Take another connecting wire and connect it to the opposite screw on the Bulb 2 mount and to the (negative) -terminal. This should light up Bulb 2 when the connecting wires are attached. Figure 2: Single Lit Bulb Student Activity Sheet Circuit Board 2

4 Figure 3 Disconnect the connecting wire from the (negative) -terminal and connect it to a screw on Bulb 3. Now take a third connecting wire and connect it to Bulb 3 and to the (negative) -terminal. Figure 2 shows two light bulbs in series. Now disconnect one of the connecting wires (does not matter which one). Observe what happens. Remove all connecting wires Figure 3: Two Lit Bulbs in Series Student Activity Sheet Circuit Board 3

5 Figure 4 Take one connecting wire and attach it to the (positive) + terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on Bulb 1 mount. Take another connecting wire and connect it to the other screw on Bulb 1 mount and to the (negative) - terminal. Now repeat this with a Bulb 3. Figure 4 shows two light bulbs in parallel. Now disconnect one of the connecting wires (does not matter which one). Observe what happens. Remove all connecting wires Figure 4: Two Lit Bulbs in Parallel Student Activity Sheet Circuit Board 4

6 Figure 5 Take one connecting wire and attach it to the (positive) + terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on Bulb 2 mount. Take another connecting wire and connect it to the other screw of Bulb 2 mount. Take the other end of the same connecting wire and to Bulb 1 mount. Take another connecting wire and connect it to the other screw of Bulb 1 mount. Take the other end of the same connecting wire and to Bulb 3 mount. Take another connecting wire and connect it to the other screw on Bulb 3 mount. Take the other end of the same connecting wire and connect to the (negative) -terminal. Figure 5 shows three bulbs in series. Remove all of the connecting wires Figure 5: Three Lit Bulbs in Series Student Activity Sheet Circuit Board 5

7 Figure 6 Take one connecting wire and attach it to the (positive) + terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on Bulb 1 mount. Take another connecting wire and connect it to the other screw on Bulb 1 mount and to the (negative) - terminal. Repeat with Bulb 2. Repeat with Bulb 3. Figure 6 shows three bulbs in parallel. Figure 6: Three Lit Bulbs in Parallel Student Activity Sheet Circuit Board 6

8 Figure 7a Disconnect the connecting wire from the (positive) +terminal and Bulb 1. Disconnect the connecting wire from Bulb 2 and the (negative) -terminal and connect it to a screw on Bulb 1. Figure 7a: Combination with Three Bulbs (All Lit) Student Activity Sheet Circuit Board 7

9 Next use 3 bulbs and show combinations of series and parallel. o Can you make 2 bright, 1 dim, etc. o Examples of this looks like: Figure 7a: Combination with Three Bulbs (Two Lit) Figure 7a: Combination with Three Bulbs (None Lit) Student Activity Sheet Circuit Board 8

10 Figure 8 Remove all connecting wires. Take one connecting wire and attach it to the (positive) +terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on the Bulb 1 mount. Take another connecting wire and connect it to the opposite screw on the Bulb 1 mount and to the side screw of Switch 2 When the switch is down the circuit is complete and Bulb 1 will light up. When the switch is up, the circuit is broken and the bulb will not light up. o The next diagram is of a switch. When power is connected to the top or side points and the switch is up, power is supplied to the top two points and each side point. Figure 8: Cold and Hot Switch Diagrams Student Activity Sheet Circuit Board 9

11 Figure 9 and 10 Can you make a series/parallel circuit using a switch? Now add a third light using a switch. See what types of circuits you can create using both switches Can you light up just bulb 1 or just 2 and 3, etc Figure 9: Two Bulbs in Series with Switch Figure 10: Two Lit Bulbs in Parallel with Two Switches Clean up: Make sure that all pieces of the circuit board are still in place and return the board to the teacher. Student Activity Sheet Circuit Boards 10

12 Activity 2: Electro magnet Useful Terms for Electro Magnet Activity: Current: flow of electric charge Amperage: the rate of flow of a current of electricity expressed in amperes Magnetic Field: a force that attracts or repels electrons and is produced when an electrical charge flows through wire Supplies: Thin wire (two foot lengths provided by teacher), a long nail or long bolt, two 1.5 volt C-cell batteries, paper clips 1. See if the nail/bolt will pick up paper clips. 2. Leave a 4 inch length of copper wire, then start wrapping the copper wire around the nail/bolt leaving at least a 4 inch length at the end. Try to make as many coils as possible without overlapping it. A single layer of wire is all that is necessary. 3. See if the nail/bolt wrapped in copper wire will pick up paper clips. 4. Connect the batteries from the circuit board to the wires at each end. 5. See if the electro magnet attracts paper clips. Clean up: Give all materials back to teacher. Student Activity Sheet Electro magnet 1

13 Activity 3: Motors Useful Terms for Motors: Current: flow of electric charge Amperage: the rate of flow of a current of electricity expressed in amperes Magnetic Field: a force that attracts or repels electrons and is produced when an electrical charge flows through wire Supplies: Coil of wire, battery, magnet 1. Use special caution when handling the coil, trying not to bend any part of it. If it is bent, it will not to work. 2. Place magnet in slot at top of battery holder. 3. Set the coil of wire on the stand over the magnet. 4. Connect the battery to the assembly. 5. Hold another magnet in various positions about the coil Clean up: Give all materials back to teacher. Student Activity Sheet Motor 1

14 Teacher Lecture Material Appendix 1: Circuit Board Teacher Instructions Pre-assembly Instructions (done by the teacher): First cut peg-board into 12 by 18 sections. Drill two holes in two of the corners of the battery mounts and use screws to screw them into the peg-board. Use another two screws to mount each switch. Do the same with the lamp mounts. Screw down a piece of thicker wire or metal shim for the terminals. Connect the battery mounts in series, with one side connected to the terminal, and the other to each switch. For safety: Cut small pieces of tubing to thread onto screws on the back of the peg-board that were used for switches, terminals and battery holders. Cut small pieces of corrugated cardboard to place over the screws on the back of peg-board that were used for the lamp mounts, then cover with duct tape. The final product should resemble Figure 1. Figure 1: Circuit Board Setup Teacher Lecture Materials Circuit Board 1

15 Standards Addressed: (PME) IV.1 e.4, (PME) IV.1 m.5 Objectives: To show students the difference between parallel and series circuits. To show students how to use a switch. Background Information: Voltage is the measure of the potential difference, and batteries are the perfect example of this. Each end of the battery is charged. Chemicals inside the battery cause the electrons to move to one end. Conventional ideology is that electrons flow from the positive point to the negative, but the opposite is true. Electrons are forced to the negative end of the battery and, when the two ends are connected in a circuit, they flow towards the positive end. This statement also infers another definition. Current is the flow of electrons. An analogy of current can be water flowing through a pipeline. Just as water flows, so do electrons. As the potential is increased like the pressure of a water pump, more electrons will flow. Resistance is anything that impedes the initial flow of electrons. Light bulbs and space heaters are two examples of large resistors. These work by using their resistance to hinder the current to produce energy that is released in the form of heat and light. Also, the wire forming the circuit and the battery both have internal resistance. Even our bodies have a large resistance to the flow of electrons, but this is true for most non-metal items. Therefore, metal objects have the least amount of resistance and are utilized for the flow of electricity. Electrical circuits operate under a few basic concepts. A potential difference is placed across an object, and electrical charge flows between the points. What makes a circuit important is that electrical equipment can be placed in line with the flow of charge to operate. Circuits can also be set up in several ways to accommodate for multiple components. Series is an arrangement of the parts of or elements in an electric circuit whereby the whole current passes through each part or element without branching. Two light bulbs in series mean that the light bulbs are connected in a straight line with each other where the electricity has to flow through one bulb to get to the other. The positive end of one bulb is connected to the negative of the other. The benefit of series circuits is that the current never changes. Two disadvantages are that the voltage decreases as it passes each light bulb or resistor, and if a bulb is removed, the circuit is broken, current cant flow to the other end of the battery, and the rest of the circuit wont work. A parallel circuit is a closed electrical circuit in which the current is divided into two or more paths and then returns via a common path to complete the circuit. When a circuit is in parallel, multiple lines connect each end of the battery. Teacher Lecture Materials Circuit Board 2

16 Parallel also represents how the light bulbs are placed in the circuit. The positive end of one bulb is connected to the positive end of the other and the negative ends are connected to each other. Now if one bulb is broken or removed, the other will still work. This is because the battery is still connected to the other light bulb. Another advantage to parallel is that a higher voltage is maintained across each of the multiple lines. The main disadvantage is that the current decreases as it is divided between the lines, which decrease the number of light bulbs you can effectively operate on each leg of the circuit. Examples: A house is a good example of an operating parallel circuit. When a light or a T.V. is turned off, the rest of the house still has electricity. If the house were in series, every appliance would have to be turned on for the whole house to have electricity. This is because current must always have a path to flow to the battery, or the circuit is broken and electricity won t flow. Because electricity follows the path of least resistance, it is easy for a short circuit to occur. If a bare wire with no light bulbs attached to it is connected to the two ends of the circuit, most of the current will travel through it rather than the rest of the circuit. This will cause the other light bulbs to not have enough current to power them. Understanding circuits and electricity will help show students how many things involved in our daily lives are affected by science. Teacher Instructions: Start off showing the kids how to make 1 light work by demonstrating on the board provided for the teacher. Then show how to put 2 lights in series, and then 2 in parallel. Allow them time to experiment with the board on their own and develop hypotheses for how and why things work on the board. Ask questions to get the students thinking about the differences between parallel and series: brightness change (bulbs are brighter in parallel), what happens if one light in series is taken out as opposed to what happens if light in parallel circuit is taken out. The figures and explanation position wires to specific bulbs, different bulb can be used as long as the same pattern is used. Single Lit Bulb (figure 2) Take one connecting wire and attach it to the (positive) +terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on the Bulb 2 mount. Take another connecting wire and connect it to the opposite screw on the Bulb 2 mount and to the (negative) -terminal. This should light up Bulb 2 when the connecting wires are attached. Two Lit Bulbs in Series (figure 3) Disconnect the connecting wire from the (negative) - terminal and connect it to a screw on Bulb 3. Now take a third connecting wire and connect it to Bulb 3 and to the (negative) -terminal. Figure 2 shows two light bulbs in series. Now disconnect one of the connecting wires (does not matter which one). Observe what happens. Remove all connecting wires Teacher Lecture Materials Circuit Board 3

17 Two Lit Bulbs in Parellel (figure 4) - Take one connecting wire and attach it to the (positive) + terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on Bulb 1 mount. Take another connecting wire and connect it to the other screw on Bulb 1 mount and to the (negative) - terminal. Now repeat this with a Bulb 3. Now disconnect one of the connecting wires (does not matter which one). Observe what happens. Remove all connecting wires Using an analogy may help the students understanding of the circuits. Explain this by the water flowing through pipes analogy. Describe electrical current as water, the wires as pipes, and the bulbs as things that resist flow of water. When the pipes in series are disconnected, the water cannot flow back to the source. Also when in parallel, the water is not slowed down by the first light it encounters. Next use 3 bulbs and show combinations of series and parallel. Test to see if they can set up 2 in parallel and 1 in series, and how could they tell by looking at the brightness of the lights. Three Lit Bulbs in Series (figure 5) - Take one connecting wire and attach it to the (positive) + terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on Bulb 2 mount. Take another connecting wire and connect it to the other screw of Bulb 2 mount. Take the other end of the same connecting wire and to Bulb 1 mount. Take another connecting wire and connect it to the other screw of Bulb 1 mount. Take the other end of the same connecting wire and to Bulb 3 mount. Take another connecting wire and connect it to the other screw on Bulb 3 mount. Take the other end of the same connecting wire and connect to the (negative) -terminal. Remove all of the connecting wires Three Lit Bulbs in Parallel (figure 6) - Take one connecting wire and attach it to the (positive) + terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on Bulb 1 mount. Take another connecting wire and connect it to the other screw on Bulb 1 mount and to the (negative) - terminal. Repeat with Bulb 2. Repeat with Bulb 3. Combination with Three Bulbs (All Lit, Two Lit, and None Lit) (figure 7a -3 versions) Disconnect the connecting wire from the (positive) +terminal and Bulb 1. Disconnect the connecting wire from Bulb 2 and the (negative) -terminal and connect it to a screw on Bulb 1. Next use 3 bulbs and show combinations of series and parallel. Can you make 2 bright, 1 dim, etc. Cold and Hot Switch Diagrams (figure 8) - Remove all connecting wires. Take one connecting wire and attach it to the (positive) +terminal (by attaching the clip to the terminal wire). Take the other end of the same connecting wire and attach it to one of the screws on the Bulb 1 mount. Take another connecting wire and connect it to the opposite screw on the Bulb 1 mount and to the side screw of Switch 2. When the switch is down the circuit is complete and Bulb 1 will light up. When the switch is up, the circuit is broken and the bulb will not light up. The next diagram is of a switch. When Teacher Lecture Materials Circuit Board 4

18 power is connected to the top or side points and the switch is up, power is supplied to the top two points and each side point. Two Lit Bulbs in Series with One Switch (figure 9) and Two Lit Bulbs in Parallel with Two Switches (figure 10) - Can you make a series/parallel circuit using a switch? Now add a third light using a switch. See what types of circuits you can create using both switches. Can you light up just bulb 1 or just 2 and 3, etc. For lead-in discussion: Ask students what they think circuits are/what they are used for. Ask for examples of different ways that they are used in everyday life. Teacher Lecture Materials Circuit Board 5

19 Appendix 2:Electro Magnet Teacher Instructions Pre-assembly Instructions (done by the teacher): Cut enough two foot lengths of bare copper wire so that each group has a copper wire. Standards Addressed: (PMO) IV.3 m.4 Objectives: To show students how to make an electro magnet. Background Information Electro magnets are just like permanent magnets except they only work when electric current is flowing through the wire. The figure below (left) shows the shape of the magnetic field around the wire. In this figure, imagine that you have cut the wire and are looking at it end-on. The green circle in the figure is the cross-section of the wire itself. A circular magnetic field develops around the wire, as shown by the circular lines in the illustration below. The field weakens as you move away from the wire (so the lines are farther apart as they get farther from the wire). You can see that the field is perpendicular to the wire and that the field's direction depends on which direction the current is flowing in the wire. Figure 11: Magnetic Fields One way to amplify the strength of the magnetic field is to coil the wire. The picture on the right is an illustration of a coiled wire. If you coil this wire around a nail/bolt, then the nail/bolt has a magnetic field around it and becomes magnetized. Teacher Instructions Electro magnets will be created by the students. They will be given a nail/bolt and two feet of wire. They will wrap the wire around the nail/bolt as much as possible without overlapping the wire. Keep the two ends of the wire exposed so that it can be attached to the batteries on the circuit board. Teacher Lecture Materials Electro Magnet 1

20 For lead-in discussion: Ask students how they think magnets are formed. Are they found in nature or are they made? Or both? (Magnets are formed in nature and can also be created synthetically. They can be found naturally occurring in objects such as rocks or can be created from metals such as iron, steel, and nickel.) Teacher Lecture Materials Electro Magnet 2

21 Appendix 3: Motor Teacher Instructions Pre-assembly Instructions (done by the teacher): 1. Unwrap the wire and straighten out any bends. Leaving about two inches straight, (about the length of a D-cell battery), wrap the wire around the battery to form a coil. (Figure 1) Unwrap a small amount from the second end so that you now have about two inches of wire sticking out from either side. (Figure 2) Figure 1 Figure 2 2. Each end of the wire is wrapped tightly around the coil for two turns. (Figure 3) This will keep the coil together. The two ends should stick out directly opposite of each other and should be at least one inch long. Excess can be trimmed or wrapped around the coil as additional turns. Figure 3 3. The wire is covered with an enamel coating for insulation. Hold the coil vertically and then rest one of the wire ends n a flat surface. (Figure 4) Using the edge of a metal support, scrape the enamel coating off the entire top half of the wire end. Turn the coil slightly as you scrape so that the top half of the wire is scraped bare. Do not scrape the bottom half of the wire. Repeat this for the second wire sticking out from the opposite end of the coil. The enamel is left on the bottom half of each wire. (Figure 5) Figure 4 Figure 5 4. Slide the metal supports up through the slots in the plastic base. The bump in the metal faces towards the battery. (Figure 6) Teacher Lecture Materials Motor 1

22 Standards Addressed: (PME) IV.1 e.4 Figure 6 Objectives: To show students how a motor works. Background Information The motor is a loop of wire that is connected to a battery and suspended over a magnet. Electric motors exist to convert electrical energy into mechanical energy. This is done by way of two interacting magnetic fields. A stationary field is created by a magnet and attached to the base of the motor. The wire coil produces the other field when electricity is passed through it, which is shown in the figures above. Electric motors, like the electro magnet, operate only when an electric current is passed through the loop. Teacher Instructions Have students connect the battery and put the magnet into the designated hole. Then have students place the loop of wire onto the wire brackets. For lead-in discussion: Ask students ideas about what a motor is/how a motor could be created. Brainstorm ideas of how a motor could be created with the objects provided for this experiment. After students have thought through the experiment on their own; show the correct way to make a motor from the objects. Teacher Lecture Materials Motor 2

23 Appendix 4: Additional Information for the Teacher Definitions: Voltage: potential difference across an object measured in volts Current: flow of electric charge Amperage: the rate of flow of a current of electricity expressed in amperes Terminal: a device attached to the end of a wire or cable or to electrical equipment for making connections Circuit: the complete path of an electric current Resistor: any object that resist the movement of electrical charge Series: an arrangement of the parts of or elements in an electric circuit whereby the whole current passes through each part or element without branching Parallel: an arrangement of electrical devices in a circuit in which the same potential difference is applied to two or more branches Magnetic Field: a force that attracts or repels electrons and is produced when an electrical charge flows through wire Other Notes for the Teacher: -Only minor construction and rearranging will be required for students to perform the experiments. -A few hours to half a day would be appropriate for these activities. A science day with a circuitry/magnetism/electricity theme would be suitable. -A literacy component can be integrated into these activities in many different ways. One way would be to have students write out their own hypothesis about what will happen in each of the experiments before they complete the experiment. This will give the students a chance to write about the experiments using what they know already. They could then share their predictions with other students and see if their ideas change after talking with classmates about their predictions. Another way to integrate a writing project would be to have the students write a letter to a friend explaining what they learned about circuitry/magnetism/electricity that day. Students could also create a game that utilizes their knowledge about circuitry/magnetism/electricity and share their game with another class that did not have a science day. Teacher Lecture Materials Additional Information 1

24 Appendix 5: Cost Estimate Circuit Needed per Unit Cost per Unit Needed per Ten Units Total Cost Peg Board (18 x 18)in 1 $ $6.32 Connector Wires 10 $ $51.90 Knife Switch 2 $ $59.80 Flash Light Bulb 3 $ $46.20 C-cell Batteries 3 $ $24.69 Battery Mounts 3 $ $29.70 Bare Copper Wire (ft) 8 $ $12.64 Totals $23.13 $ Electro Magnet Needed per Unit Cost per Unit Needed per Ten Units Total Cost 3in Nails or bolts 1 $ $0.40 Bare Copper Wire (ft) 2.5 $ $4.64 C-cell Batteries 3 $ $24.69 Battery Mounts 3 $ $29.70 Masking Tape (Rolls) 1 $ $1.14 Knife Switch 1 $ $29.90 Paper Clips 10 $ $0.97 Totals $10.17 $91.44 Electric Motor Needed per Unit Cost per Unit Needed per Ten Units Total Cost Electric Motor 1 $ $33.30 Totals $3.33 $33.30 Individual Experiments Used in other Cost w/ reuse of Bulk Purchase Price Individual Cost Item Location Reusable? experiments some parts 8.99 per 32ft 2 $0.632 Lowes yes no $8.99 $5.19 per package $0.519 Radio Shack yes yes $51.90 $2.99 each $2.990 Radio Shack yes yes $59.80 $1.54 each $1.540 Walmart yes no $46.20 $9.88 per package $0.823 Sam's Club yes yes $24.69 $0.99 each $0.990 Radio Shack yes yes $29.70 $12.63 per 80ft Coil $0.158 McMaster-Carr yes no $12.63 $ Bulk Purchase Price Individual Cost Item Location $1.84 per lb $0.040 Lowes yes no $ per 20ft Coil $0.186 McMaster-Carr yes no $3.71 $9.88 per package $0.823 Sam's Club yes yes $0.99 each $0.990 Radio Shack yes yes $6.86 per 6 $1.140 Sam's Club no yes $2.99 each $2.990 Radio Shack yes yes 0.97 per box $0.010 Walmart yes no $0.97 $ Bulk Purchase Price Individual Cost Item Location $33.30 for 10 $3.330 Nasco yes no $33.30 $52.70 Total Cost: $ Teacher Lecture Materials Cost Estimate 1

25 Student Activity Sheet Name Create Your Own Hypothesis Circuit Boards Create your own hypothesis (theory) about what will happen when we connect the different items on the circuit boards. What do you think is the difference between parallel and series? Student Activity Sheet Circuit Board 1

26 Student Activity Sheet Name Activity 1: Circuit Boards 1. What does it mean when an electrical current is in parallel? 2. What does it mean when an electrical current is in series? 3. What does the switch do on a circuit board? 4. Where can you find circuits in real life? Student Activity Sheet Circuit Board 2

27 Student Activity Sheet Name Create Your Own Hypothesis Electro magnets How do you think magnets are formed? Student Activity Sheet Electro magnet 1

28 Student Activity Sheet Name Activity 2: Electro magnet 1. How can you make your own magnet? 2. Why did our electro magnet work? 3 Put an X in front of items that were magnetic: cooper wire pop can CD shiny nut shiny pan pencil (any part?) yellow ruler silver wire clothes pin (any part? 4 What other things did you try and were they magnetic? Student Activity Sheet Electro Magnet 2

29 Student Activity Sheet Name Activity 3: Motor 1. Explain how we made a motor out of the wire, battery, and magnet. 2. Motor Why does the wire move? How does this create a motor? Student Activity Sheet Motor 1

30 Student Activity Sheet Name A Letter to a Friend Write a letter to a friend explaining what you learned today about circuit boards, magnetism, and electricity. Write about the experiments that you completed and what you learned from the experiments. Dear, Sincerely,