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Microsoft Word Doc - Build a Simple Ammeter SK#5

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Microsoft Word Doc - Build a Simple Ammeter SK#5

    Solar Kit Lesson #5

    Build a Simple Ammeter

    TEACHER INFORMATION

LEARNING OUTCOME

    After building and working with a simple ammeter, students are able to describe the relationship

    between the direction of a current and the magnetic field it produces.

LESSON OVERVIEW

    In this lesson, students:

    ? propose and test theories on why solar cells connected in parallel produce more current

    than in series; and

    ? apply conventional standards of (a) clockwise analog meter movement and (b) electrons

    flowing from a negative terminal. Students build a simple ammeter to indicate the presence, direction, and strength of an electric

    current flowing through a wire. This device may be used later on to help students design and

    build a solar-powered battery charger in the Solar Kit lesson Solar-Powered Battery Charger.

GRADE-LEVEL APPROPRIATENESS

    This Level II Physical Setting lesson is intended for use in physical science and technology

    education classes in grades 59.

MATERIALS

    Per work group

    ? 150 cm enamel-coated magnet wire

    ? 2.5 cm length of drinking straw

    ? compass

    ? 2 large (―jumbo‖) metal paper clips straightened and cut into six 5 cm long pieces of ―wire‖

    ? 15 x 40 cm piece of cardboard or card stock

    ? masking tape

    ? scissors

    ? two 1 V, 400 mA minisolar panels* with alligator clip leads ? gooseneck lamp with 150-watt incandescent bulb

* Available in the provided Solar Education Kit, other materials are to be supplied by the teacher.

SAFETY

    Warn students that the bulb will become hot enough to cause a burn if touched. If a battery is

    used to power the electromagnet, it should be connected for only short periods of time. Warn

    www.SchoolPowerNaturally.org

students that if it is connected over a longer period, the battery or wire may get hot enough to

    cause a burn, and the battery will discharge quickly. Connecting an electromagnet to a mini

    solar panel, however, poses no safety hazards.

TEACHING THE LESSON

    Preparation: Prepare the workgroup materials. Use a pair of diagonal cutters to cut the jumbo paper clips into 5 cm long pieces and scissors to cut drinking straws into 2.5 cm long pieces.

Students should work in groups of two or more. Set out all materials but hold back one of the

    minisolar panels at each of the workstations.

The basic concepts for an electromagnet are described in the student handout. If you need to

    familiarize yourself with these concepts, read the handout before holding the classroom

    discussion. Ask students to describe what they already know about electromagnets. Tell students

    that they will use such information in this activity to design and build a device to indicate the

    presence, direction, and strength of a current flowing from one or two solar panels. Pass out the

    handout and have students follow the directions.

Between steps 1 and 2, you may want to allow time for students to test their electromagnet by

    using a battery (for a current source) to pick up metal paper clips. Remember to warn students to

    connect the battery for only a short period of time.

Step 6 asks students to make a prediction expressed through a drawing. Tell them that after they

    complete their prediction, you will check their work and provide them with the second mini

    solar panel.

Review Discussion:

    Review with the students that the electromagnet exerts a force on the compass needle.

Discuss with students how a pointer swinging in a clockwise direction, by convention, describes

    a positive increase in value. Think of a speedometer on a car. Have students connect a solar

    panel so that the compass needle swings clockwise (toward the east). Then have them mark the

    terminal connected to the black wire with a minus (-) sign and the terminal connected to the red

    wire with a plus (+) sign.

Ask students to share their explanations of why parallel solar cells produce the most current.

    Help them understand that a solar cell limits the amount of current that flows through it.

ACCEPTABLE RESPONSES FOR DEVELOP YOUR UNDERSTANDING SECTION

    1) The finished electromagnet will have two 5 cm wire leads with the insulation removed.

    2) Lamp and solar cell will be positioned as described in the handout.

    3) Students can show that turning the light on and off will cause the compass needle to

    shift by 15 to 20 degrees.

    4) The compass needle deflects in the opposite direction.

    Build a Simple Ammeter 2

    Physical Setting; physical science, technology education; Level II

    5) Arrows are drawn on the ammeter pointing along the two terminals. One terminal is

    marked with an E, the other with a W. Given a solar panel connected with either

    polarity, students can predict which way the compass needle will deflect.

    67) Responses will vary in this part of the activity, but the diagram will typically show the

    two solar panels connected in parallel with the ammeter. Students will likely offer the

    following reason for connecting the panels in parallel: When solar panels are

    connected side by side (in parallel), the electrons from the second panel don’t have to

    go through the higher resistance of a first solar panel, as they would if the panels were

    connected front to back (in series).

ADDITIONAL SUPPORT FOR TEACHERS

    SOURCE FOR THIS ADAPTED ACTIVITY

    The idea of using an electromagnet and a compass to form a simple ammeter came from “Thames & Kosmos Power House Experiments in Future Technics Experiment Manual,”

    produced by Thames & Kosmos, LLC, Newport, RI, 2001.

    BACKGROUND INFORMATION

    Ammeters are designed with the use of a sensitive current detector. In this case, the current

    detector is a compass needle (a small magnet), held in the variable magnetic field of an

    electromagnet. As current in the electromagnet varies, so does the force on the compass needle.

Electricity flowing through a wire creates a magnetic field around that wire. Wrapping that wire

    in a coil creates an electromagnet. Wrapping the wire around a material that can be magnetized

    iron objects, for exampleturns such material into a magnet and effectively amplifies the

    magnetic field formed by the wire coil.

In this lesson, students use the magnetic field around a wire to create an electromagnet that is

    used to deflect a compass’s magnetic needle, forming a simple ammeter. During the lesson they

    may notice that some of the paper clip wire has become semipermanently magnetized. Their

    design will need to compensate for this by adjusting the position of the ammeter on the table.

Commercial analog ammeters use a galvanometer as a sensitive current detector. A galvanometer

    contains a small coil attached to a spring placed in a fixed magnetic field. When current flows

    through the coil, magnetic attraction turns the coil against the pull of the spring. The coil is

    attached to the pointer of the analog meter.

    REFERENCES FOR BACKGROUND INFORMATION

    Georgia State University. C. R. Nave. HyperPhysics website:

    http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Build a Simple Ammeter 3

    Physical Setting; physical science, technology education; Level II

    LINKS TO MST LEARNING STANDARDS AND CORE CURRICULA

Standard 1Analysis, Inquiry, and Design: Students will use mathematical analysis,

    scientific inquiry, and engineering design, as appropriate, to pose questions, seek answers, and develop solutions.

     Scientific Inquiry Key Idea 1: The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing, creative process. (elementary and intermediate)

     Key Idea 2: Beyond the use of reasoning and consensus, scientific inquiry involves the testing of proposed explanations involving the use of conventional techniques and procedures and usually requiring considerable ingenuity. (elementary)

     Key Idea 3: The observations made while testing proposed explanations, when analyzed using conventional and invented methods, provide new insights into phenomena. (elementary)

     Engineering Design Key Idea 1: Engineering design is an iterative process involving modeling and optimization (finding the best solution within given constraints); this process is used to develop technological solutions to problems within given constraints. (elementary and intermediate)

Standard 3Mathematics: Students will understand mathematics and become mathematically

    confident by communicating and reasoning mathematically, by applying mathematics in real-world settings, and by solving problems through the integrated study of number systems, geometry, algebra, data analysis, probability, and trigonometry.

     Measurement Key Idea 5: Students use measurement in both metric and English measure to provide a major link between the abstractions of mathematics and the real world in order to describe and compare objects and data. (elementary and intermediate)

Standard 4The Physical Setting: Students will understand and apply scientific concepts,

    principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

     Key Idea 3: Matter is made up of particles whose properties determine the observable characteristics of matter and its reactivity. (elementary)

     Key Idea 4: Energy exists in many forms, and when these forms change

    energy is conserved. (elementary and intermediate)

     Key Idea 5: Energy and matter interact through forces that result in changes in motion. (elementary and intermediate)

Standard 5Technology: Students will apply technological knowledge and skills to design,

    construct, use, and evaluate products and systems to satisfy human and environmental needs.

     Key Idea 1: Engineering design is an iterative process involving modeling and optimization used to develop technological solutions to problems within given constraints. (elementary)

     Key Idea 2: Technological tools, materials, and other resources should be selected on the basis of safety, cost, availability, appropriateness, and environmental impact; technological processes change energy, information, and material resources into more useful forms. (elementary and intermediate)

Build a Simple Ammeter 4

    Physical Setting; physical science, technology education; Level II

Standard 6Interconnectedness: Common Themes: Students will understand the

    relationships and common themes that connect mathematics, science, and technology and apply

    the themes to these and other areas of learning.

     Key Idea 3: The grouping of magnitudes of size, time, frequency, and pressures or other

    units of measurement into a series of relative order provides a useful way to deal with the

    immense range and the changes in scale that affect the behavior and design of systems.

    (elementary and intermediate)

     Key Idea 5: Identifying patterns of change is necessary for making predictions about

    future behavior and conditions. (elementary and intermediate)

Produced by the Northeast Sustainable Energy Association in coordination with the Research

    Foundation of the State University of New York with funding from the New York State Energy

    Research and Development Authority (NYSERDA)

    www.nyserda.org

    Should you have questions about this activity or suggestions for improvement, please

    contact Chris Mason at cmason@nesea.org.

    (STUDENT HANDOUT SECTION FOLLOWS) Build a Simple Ammeter 5

    Physical Setting; physical science, technology education; Level II

Name ___________________________________

    Date ____________________________________

    Build a Simple Ammeter

In an upcoming lesson, you will design a solar-powered battery charger. But first, you need a

    way to test whether that battery charger is delivering electrons to the proper terminal of a dead

    battery. To do this, you now will build a simple ammeter that indicates the presence, direction,

    and strength of an electric current flowing through a wire.

Here is information useful for completing this task:

    1. Electricity flowing through a wire creates a magnetic field around that wire.

    2. Wrapping that wire in a coil concentrates this field in a small space, making what is known

    as an electromagnet.

    3. Wrapping the wire around a material that can be magnetizediron objects, for example

    turns such material into a magnet and effectively amplifies the magnetic field formed by the

    wire coil.

    4. A magnetic field can move a magnet such as a compass needle.

    1) Build a small electromagnet. Tape off one end of the straw. Tightly wrap the provided wire

    around 2.5 cm of drinking straw, leaving about 5 cm of each end of the wire unwrapped. If

    you run out of room on the straw, start another layer on top of the one just completed. When

    all the wire is wrapped, tape the wire in place. With scissors, scrape the insulation from the

    last 1 cm of both ends of the wire. The strength of this electromagnet can be adjusted by

    inserting various types and amounts of materials that can be magnetized (such as the wire

    used to make paper clips) into the coil.

    2) Current source: Tape one minisolar panel to the table and position the 150-watt lamp 120

    cm above the panel. Do not place the lamp any closer as it may melt the panel’s plastic cover.

    Turn the lamp on only while taking a measurement.

    Figure 1

     W S N E

    1

3) Build the ammeter. See figure 1. You are to construct a device that will deflect a compass

    needle 15 to 20 degrees when powered by the current source described above. Connect the

    solar cell leads to the two electromagnet leads.

    Tape the compass to one end of the piece of cardboard so that the east-west axis is parallel to

    the long axis of the cardboard. Make sure that the north half of the compass face is visible.

    Position the electromagnet next to the compass. Adjust its position and the number of

    inserted paper clip wires to produce a device that will deflect the compass needle 15 to 20

    degrees when the light is turned on.

    When you have a working device, tape the electromagnet to the cardboard and the cardboard

    to the table.

    4) Test for the direction of a current. Switch the solar panel’s red and black wires. What do

    you see? Why?

    5) Calibrate your ammeter for direction of current. On your ammeter, indicate the direction

    in which electrons flow to deflect the compass needle

    1) toward the west compass mark and

    2) toward the east compass mark.

    Previously you learned that electrons flow from the top of a solar cell, making the top the

    negative terminal of a cell. By convention (artificial agreement), the black wire is connected

    to the negative terminal of the solar panel and the electrons flow out of the black wire.

    Next to the terminal that is connected to the solar panel’s black wire, draw an arrow

    indicating the direction in which the electrons are flowing. Next to the arrow, write a W if the

    compass needle is deflected toward the west compass mark and an E if it is deflected toward

    the east mark. Swap red and black wires and repeat.

    6) Make a prediction. Draw a diagram that predicts how to connect two minisolar panels to

    the ammeter so that the current is the greatest. Explain why you would connect the panels in

    this way. [Hint: Think of the electrons that are being energized by the light as workers

    traveling to their place of work, each in his or her own car.]

Build a Simple Ammeter 2

    7) Test for strength of current. Tape the two solar panels to the table side by side. Position the

    lamp so it is the same distance from both panels. Again, do not place the lamp any closer to

    the panels than 120 cm or it may melt a panel’s plastic cover.

    Connect the two solar panels to the electromagnet in many different ways. For each way,

    draw a diagram to predict how the panels are connected. Make sure to indicate red (positive)

    and black (negative) wires. For each, write down in which direction and how far the

    compass’s needle is deflected. Circle the diagram that produces the most current (deflects the

    compass needle the most when the light is turned on). Does it match your prediction? If it

    does not, give a revised reason to explain why this configuration produces the most current.

    Extension Activity. Modify the design of your ammeter so that it can be used to test the strength of an AA battery.

Caution: Connect a battery to your ammeter for only a short time. If you leave it connected for

    too long, the battery and the wire might overheat and cause a burn, plus the battery will

    discharge rapidly.

Solar panels self-limit the amount of current they produce. Household batteries can produce a

    much larger current when shorted. For this reason a battery would ―peg‖ the ammeter you just

    built, making it useless as an indicator of strength. How might you modify the design of your

    ammeter so that it would work with a higher current device such as an AA battery?

Build a Simple Ammeter 3

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