Electricity and Magnetism Teacher Guide

Unit

Electricity and Magnetism

Subject

Physical Science

Grade Level

ES 3-4

Activity Name(s)

Conductors and Insulators

Lighting a Bulb

Magnets and Coils

Being Prepared

The activities in this unit are best set up in small groups, with 2-4 students in each group. The teacher might find it beneficial to model the diagrams using a projector to ensure the students understand the set up procedures.

Use caution with batteries; they have the potential to get very hot when both poles are in contact with conductive material.

Keep all magnets away from computers, cell phones, and electronic devices.

Be very careful when using strong rare earth magnets since they can cause pinching if fingers are caught between two magnets or between a magnet and steel objects such as desks or chair legs.

Getting Started

All activities use the voltage sensor. Some of the data may generate very small values, so you may have to adjust the unit size of the data in order to make the data meaningful.

Be sure to run the activity using the equipment that the students will be using to ensure everything will run smoothly.

Materials such as small holiday lights can often be purchased cheaply at dollar stores or after the holidays. Having a parent or aide cut the bulbs apart and strip wire ends will make the process run smoothly. Note that you may go through a lot of bulbs depending on the quality of bulbs. If alligator clips are not available you could also have a parent or aide cut and strip wire for the activities.

A variety of magnets are needed for the Magnets and Coils activity. Ceramic magnet, alnico, or rare earth magnets can be purchased through a variety of science supply companies. In addition you will need 50 feet of hook-up or magnet wire (22-28 gauge). This can also be purchased through science supply companies.

Suggested Timeline

The Conductors and Insulators and Lighting a Bulb activities can be completed in one 45-50 minute class period. The Magnets and Coils activity may take two short class periods or one block period. In the Magnets and Coils activity, the students will use probeware to collect voltage data, and also use a PhET model to gather information, thus taking more time to complete.

Thinking about the Discovery Questions

The activities in this unit introduce students to concepts relating to electricity and magnetism. They will begin by exploring the differences between conductors and insulators in the activity "Conductors and Insulators" they begin with the question "Which materials conduct electricity and which do not?". As they answer this question the activity will help show the students that no energy is transferred when when the circuit is incomplete or open. Students will explore with building circuits in series and parallel while collecting data on the voltage generated. They will be able to distinguish between an open and closed circuit, and classify items that are conductors and insulators.

In the second activity "Lighting a Bulb" students explore the answer to the question "What different circuits will light a bulb with a battery?". Building parallel and series circuits they will attempt to light a small bulb using a battery. They will measure the voltage across the circuits to find the efficiency of their circuits.

In the Magnets and Coils activity, students will be exploring how the electric current can be generated using a magnet and coil. Using the question "How can you produce electricity using only wire and a magnet?", the students will manipulate the two items and collect voltage data to determine what factors are most important in generating voltage. This concept can be difficult for students to understand, but working with the materials will allow them to see that magnets have invisible fields which apply a force.

Misconceptions

Electricity and magnetism are very abstract concepts for students to understand. Many misconceptions may come up that need to be addressed over the course of this unit. One of the most persistent and stubborn misconceptions is that electricity is "used up" as it moves around a circuit. Water pump models (often used to explain electricity to children) can actually promote this misconception of "used up electricity". Many students erroneously tend to think that the battery is the source of the current and that the circuit is initially empty of the stuff that flows through the wires. It helps if young students can use drawings and diagrams to visualize what happens when electric current flows through a wire (conductor) connected to an energy source (battery). To produce current, there must be a closed circuit loop and a source of energy. But the atoms in the wire don't just materialize or get "used up". The atoms that make up the structure of the wire are always there and capable of producing current if energy is supplied. Another misconception is that electrical currents move in a circle. A more accurate view would be that when a bulb is connected to a battery, the electrical energy moves from the battery to the bulb in a one-way flow. Finally if students are familiar with the term conductor and insulator, they may believe that they are the same thing. Conductors and insulators have very different functions. Conductors are materials that allow electricity to flow easily, while insulators don't allow electricity to flow easily. We use conductors in electrical circuits and insulators to protect ourselves. Finally, students do not readily recognize the magnetic effect of an electric current. Some think of the wire, rather than the electric current as being the cause of the magnetic effect. Students may think that insulation around the wire prevents the existence of magnetic forces when current flows.

Learning Objectives

NGSS

• Performance Expectations
  • 3-PS2-3. Ask questions to determine cause and effect relationships of electric or magnetic interactions between two objects not in contact with each other.
  • 3-PS2-4. Define a simple design problem that can be solved by applying scientific ideas about magnets.
  • 4-PS3-2. Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents.
  • 4-PS3-4. Apply scientific ideas to design, test, and refine a device that converts energy from one form to another.
• Disciplinary Core Ideas
  • ES-PS2: Motion and Stability: Forces and Interactions
    • PS2.B: Types of Interactions
      • Electric and magnetic forces between a pair of objects do not require that the objects be in contact. The sizes of the forces in each situation depend on the properties of the objects and their distances apart and, for forces between two magnets, on their orientation relative to each other. (3-PS2- 3),(3-PS2-4)
  • ES-PS3: Energy
    • PS3.A: Definitions of Energy
      • Energy can be moved from place to place by moving objects or through sound, light, or electric currents. (4-PS3-2),(4-PS3-3)
    • PS3.B: Conservation of Energy and Energy Transfer
      • Energy is present whenever there are moving objects, sound, light, or heat. When objects collide, energy can be transferred from one object to another, thereby changing their motion. In such collisions, some energy is typically also transferred to the surrounding air; as a result, the air gets heated and sound is produced. (4-PS3-2),(4-PS3-3)
      • Light also transfers energy from place to place. (4-PS3-2)
      • Energy can also be transferred from place to place by electric currents, which can then be used locally to produce motion, sound, heat, or light. The currents may have been produced to begin with by transforming the energy of motion into electrical energy. (4- PS3-2),(4-PS3-4)
    • PS3.C: Relationship Between Energy and Forces
      • When objects collide, the contact forces transfer energy so as to change the objects’ motions. (4-PS3-3)
    • PS3.D: Energy in Chemical Processes and Everyday Life
      • The expression “produce energy” typically refers to the conversion of stored energy into a desired form for practical use. (4-PS3-4)
• Practices
  • Asking questions and defining problems
    • Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions.
  • Developing and using models
    • Develop and/or use a model to predict and/or describe phenomena.
    • Develop a model to describe unobservable mechanisms.
  • Planning and carrying out investigations
    • Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.
    • Collect data about the performance of a proposed object, tool, process or system under a range of conditions.
  • Analyzing and interpreting data
    • Analyze and interpret data to provide evidence for phenomena.
    • Analyze and interpret data to determine similarities and differences in findings.
  • Constructing explanations and designing solutions
    • Apply scientific ideas or principles to design, construct, and/or test a design of an object, tool, process or system.
• Cross Cutting Concepts
  • Cause and effect
    • Students classify relationships as causal or correlational, and recognize that correlation does not necessarily imply causation. They use cause and effect relationships to predict phenomena in natural or designed systems. They also understand that phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.
  • Scale, proportion, and quantity
    • Students observe time, space, and energy phenomena at various scales using models to study systems that are too large or too small. They understand phenomena observed at one scale may not be observable at another scale, and the function of natural and designed systems may change with scale. They use proportional relationships (e.g., speed as the ratio of distance traveled to time taken) to gather information about the magnitude of properties and processes. They represent scientific relationships through the use of algebraic expressions and equations.
  • Systems and system models
    • Students can understand that systems may interact with other systems; they may have sub-systems and be a part of larger complex systems. They can use models to represent systems and their interactions — such as inputs, processes and outputs — and energy, matter, and information flows within systems. They can also learn that models are limited in that they only represent certain aspects of the system under study.

NSES

• NSES Physical Science – Light, heat, electricity, and magnetism
  • Electricity in circuits can produce light, heat, sound, and magnetic effects. Electrical circuits require a complete loop through which an electrical current can pass.
• NSES Physical Science - Properties of objects and materials
  • Objects have many observable properties, including size, weight, shape, color, temperature, and the ability to react with other substances. Those properties can be measured using tools, such as rulers, balances and thermometers.

Discussion: Setting the Stage

• What is a conductor? What is an insulator?

  A conductor is a material that allows electrical charge to easily flow through it. An insulator is a material that does not allow electrical charge to flow through it. Children in elementary school won't be ready to understand the complexity of valence electrons, but here's a simple analogy that will help them visualize what goes on at the atomic level: The atoms in an insulating material hold tightly to their outer electrons like good parents watching their children. But the atoms in a conducting material are more like poor parents, and those outer electrons will wander off. Electrons repel each other. When one gets close to another, they quickly move apart, causing a chain reaction that lets current move freely. (Teachers: Metals are conductors because their valence electrons are loosely bound. Most solid materials are insulators because their outer electrons are so tightly bound,  they offer resistance to the flow of electric current.)

• How does current move in a wire?

        Metal wires are conductors. Metal is made up of atoms that allow outer electrons to move freely. The battery provides the energy to get the electrons moving in a continuous flow of current when the circuit is closed. If you break the circuit loop, the electrons don't "spill out" like water in a hose. They just stop moving in a continuous flow. If you reconnect the circuit, the moving flow will resume. Teachers: The physics of direct resistive current is more complicated, but this is probably all children in this age bracket can comprehend.

• What is an electric circuit?

  An electric circuit is a loop that allows electric current to flow. A circuit usually has a source of electrical energy, like a battery, and something the uses electrical energy, like a lightbulb or a motor. The loop must must be closed and continuous for the electricity to flow. That is, it must form a circle that returns to the beginning.

• What materials can be used to make an electric circuit?

  The loop must be made of electrical conductors, like wires, which allow the electric current to flow through them. If one of the parts of the loop is an insulator, the circuit won't be closed and electricity will not flow.

Discussion: Formative Questions

Conductors and Insulators

• When you connect the batteries to the wire does it make a difference which end (+ or -) is connected?

  It won't affect the flow which end of the battery and which wire in the bulb is connected, as long as the circuit is closed.

• What materials in the wire and bulb allow the current to flow?

  The materials in both are conductors such as copper or certain other metals. Teachers: You may need to watch for student misunderstanding here. Children often think of a light bulb as glass, which is an insulating material. Help them look closely to see the filament inside the bulb so they realize the filament is acting as a metal conductor of the current.....not the glass.

• Why do some materials work as insulators?

  Materials that are insulators have strong atomic bonds which prevent electrons from moving freely. Since the electrons can't move freely an electrical current can't easily pass through them.

Lighting a Bulb

• As you increase the number of bulbs in your circuit does the brightness of the bulbs change?

  Answers will vary, but some students may observe a decrease in the brightness of the bulbs.

Magnets and Coils

• What do you observe when the magnet is placed in the wire coil?

  An electric current is generated.

• Is there a way to increase the current generated by the magnet and coil?

  Yes, move the magnet in and out of the coil quickly.

• What happens when the magnet is in the coil, but not moving?

  No current is generated (the current is induced as the magnetic field changes location creating a force)

Discussion: Wrapping Up

Conductors and Insulators

• What is the difference between a conductor and an insulator?

  Conductors are materials that permit electrons to flow freely from atom to atom and molecule to molecule. An object made of a conducting material will permit charge to be transferred across the entire surface of the object. If charge is transferred to the object at a given location, that charge is quickly distributed across the entire surface of the object. In contrast, insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. If charge is transferred to an insulator at a given location, the excess charge will remain at the initial location of charging. The particles of the insulator do not permit the free flow of electrons; subsequently charge is seldom distributed evenly across the surface of an insulator.

Lighting a Bulb

• Explain the difference between an open and closed circuit.

  In an open circuit, there is a break in the loop of electric current that prevents the current from completing the loop. In a closed circuit, the current is able to flow continuously through the loop. A continuous flow of current is necessary in order to transfer energy to product electricity.

Magnets and Coils

• Can a magnet generate an electric current?

  The flow of electricity through a wire creates magnetic fields, and certain types of magnetic fields (they have to change with time) cause the flow of electricity. Generators of electricity use magnets to generate the electricity. Electric motors use both electricity and magnets to create motion. The incoming electricity provides the power and generates magnetic fields which convert the power into motion. Motors are basically the opposite of generators. One uses electricity to generate motion and the other uses motion to make electricity.

Additional Background

Excellent content support for teachers can be found in The Physics Classroom's free online tutorial "Current Electricity". It takes a deep dive into electric field, electric potential difference, requirements of a circuit, Ohm's Law and resistance, and Q & A sets to self-gauge your understanding.      http://www.physicsclassroom.com/class/circuits

Conductors and Insulators

Most metals are good conductors. They allow electrons to move freely which is necessary for an electrical current to move. Copper is a good conductor and is used because it is relatively inexpensive. Silver and gold are much better conductors and are used in many of the hand held devices we use today.

Insulators are materials that don't allow electrons to move freely. We use them to protect ourselves from getting electrical shocks. Wiring in our house are covered with plastic which is a good insulator. We have to strip off some of the plastic (insulation) when we hook the wires together to allow for the movement of electrons. Some other common insulators are rubber, wood, and paper.

Lighting a Bulb

A series circuit is one that has only path to get from one part of the circuit to another. In a series circuit if you break the path at any point the circuit will be broken. If you are trying to light 2 bulbs in a series if you disconnect one you will have an open circuit and the second bulb will go out. In a parallel circuit you have 2 or more components connected in between in the same 2 points. In a parallel circuit with 2 bulbs you could remove one and still have the other light.

Magnets and Coils

Faraday's Law: Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.

A generator is a device that moves a magnet near a wire to create a steady flow of electrons. The action that forces this movement varies greatly, ranging from hand cranks and steam engines to nuclear fission, but the principle remains the same.

Analysis

Conductors and Insulators

1. Look closely at a holiday bulb and the wires that come out of it. What parts of the bulb conduct electrical current and what parts do not conduct electrical current?

   The wires and filament in the bulb conduct electrical current, the glass and plastic parts do not.

2. Draw a picture of the wires and the bulb and label what conducts and what does not.

   Drawings will vary, but should reflect the answer in previous question.

3. What is similar about the conducting materials that you tested?

   They are all metals.

4. What is similar about the insulating materials that you tested?

   They are all nonmetals.

5. Explain why an electrical wire usually has copper on the inside with rubber or plastic around the outside.

   The rubber/plastic coating is an insulator used for protection. When electric current flows through conductive metals, it transfers electrical energy. Electrical energy can be dangerous, so we use insulators to prevent the electric current from flowing into other areas.

Lighting a Bulb

1. Which circuit is like the one you made with two lights -- circuit A (series) or circuit B (parallel)?

   Answers will vary depending on how they connected the lights. They should refer to their drawing to determine which circuit the student created.

2. In your own words, what is the difference between a parallel and series circuit?

   A series circuit only has one path for the flow of electric current. A parallel circuit has two or more paths for the flow of electric current.

Magnets and Coils

• Based on your investigations in this activity, can you produce a voltage if the magnet doesn't move? Can you produce a voltage if the coil doesn't move? Support your answers with evidence.

  Yes, as long as there is movement between the two objects (either the magnet or the coil moving) then a voltage can be produced. No voltage is produced if there is no movement between the magnet and coil. Voltage is only produced when there is a change in the magnetic field.

• Which factor was most important for producing a voltage in the coil? Explain your answer.

  d) it didn't matter which was moving.

  Explain your answer

  As long as there is movement between the two objects (either the magnet or the coil moving) then a voltage can be produced. No voltage is produced if there is no movement between the magnet and coil. Voltage is only produced when there is a change in the magnetic field.

• Based on the work you did, what voltage do you think would be produced if you held the magnet right next to the coil and waved both of them around in the air together? Explain.

  Student predictions will vary. They should mention that being placed next to each other does not induce a current, that the magnetic field must change in order to produce an electric current.

Further Investigation

Give students a variety of simple resistors (lights, bells, motors, buzzers, etc) and switches and have students create circuits (series and parallel) that can be turned on and off.

Give students hollow pipe made of nonmagnetic conductive material (ex: copper or aluminum) and a neodymium magnet that has a diameter slightly smaller than the pipe. Show the students how the magnet is not attracted to the pipe and falls to the ground at the rate of gravity (have the students time the fall). Then drop the magnet inside the pipe and have the students time the fall. Ask the students to hypothesize why the rate of fall is slower. (The magnet creates a current in the pipe as it does in the wire from the activity, which is a resistant force similar to friction, thus slowing down the magnet.)