Energy Transformation Teacher Guide

Unit

Energy Transformations

Subject

Physical Science

Grade Level

ES 5-6

Activity Name(s)

Light Bulbs

Motors and Generators

Solar Cell

Being Prepared

Students may be assigned to groups of 2-3 per computer/probe. If sufficient quantity of probes is not available, instructor may consider assigning activities within the unit to groups and then allowing time for each group to share their activity and results. If availability of solar cells is limited, the Solar Cell component may be conducted as a whole-class based activity using an LCD projector and/or interactive white board.

Note: The activities using the batteries, wire, and bulbs need to monitored since heat from these can cause burns.

Safety

Do not apply more than 1.5 V to the paper clip. It will dangerously overheat and damage the sensor.

Getting Started

Setup for the light, temperature and voltage probes is straightforward. In the "Light Bulbs" activity, caution students that the paperclip attached to the battery may become hot. Additionally, wires used to complete the circuits may also become hot. Circuits should be disconnected when data is not being collected. If you are using holiday lights consider having a parent or aide pre-cut and strip the wires. This can be a little tricky getting enough exposed wire to connect to the battery. (After holiday sales are a good time to get strings of bulbs cheap.) Make sure that you have access to both hot glue guns and glue. Having a "hot glue station" where all the hot glueing would take place may make things work more smoothly.

You will need a number of small motors, solar cells, and resistors to complete these activities. One source for these is www.kelvin.com.

Suggested Timeline

Each activity in the unit may be completed within a 45-minute class period. Be sure to allow time for student debriefing, either as a whole-group activity or in small group conferencing. If time availability is limited, instructor may consider using one of the components of the unit as a demonstration or whole-class activity.

It will be helpful for students to have an understanding of circuits prior to completing the activities in this unit. Students should also have knowledge of how the poles of magnets interact with each other (opposites attracting and likes repelling).

Materials: Light Bulbs

• temperature sensor
• small size steel paper clip
• AA battery (1.5 V - do not use a greater voltage)
• 3 V flashlight OR single holiday light
• LED flashlight
• light sensor (for Extension activity)

Materials: Solar Cell Activity

Thinking about the Discovery Questions

This unit is motivated by the discovery questions:

• How does electricity light a bulb? How is this done most efficiently?
• Can electrical energy be transformed into mechanical energy, and back again?
• How can solar energy be transformed into electrical energy?

Electrical energy is the energy carried by moving electrons in an electric conductor. You can't see it, but it is one of our most useful forms of energy because it is relatively easy to transmit and use. In the first of this 3-part lesson module, students engage in experiments to compare heat outputs of an LED bulb, a AA battery, and a holiday light bulb. Which bulb is most efficient? In the Solar Cell activity, students will attach voltage sensors to a solar cell to generate real-time graphs of voltage values over time. How does the distance from a light source affect the output of the solar cell? In the Motors and Generators activity, students experiment with very simple motors (cost is $1.00-$2.00 apiece) to figure out if electrical energy can be transformed into mechanical energy (and back again).

Safety: Given the target age group, teachers may want to ask parents to help with set-up and tear-down of the experiments. Specific safety guidelines are listed below:

• In the light bulb activity, do not use a battery of more than 1.5 volts (AA).
• Motors and Generators Activity:  Hot glue guns can cause serious burns. For this age bracket, it's recommended that teachers perform the hot glue gun to join the motor shafts. 
  

Misconceptions

Students of all ages tend to believe that energy is being used up by a device, and this misconception often remains entrenched well into the college years. Emphasize to students that the charge in a circuit is not used up or consumed. This energy is being transformed into non-electrical forms (heat, light, mechanical, etc.) The Law of Conservation of Energy states that energy may be transformed from one form to another, but is never created or destroyed. Another common misconception is that outlets (plugs) are creating the electrical energy used by electric devices, and transfer energy even when the device is turned off and there is an incomplete circuit. It's important for students to start building an accurate mental model of electric charge through a circuit. The charge that flows through a circuit originates in the wires of the circuit. We call metal wires "conducting materials" because they have an atomic structure that allows electrons to move freely and produce an electric current. Electric circuits require a complete loop through which the current can pass.

Content Support for Teachers

If you'd like a refresher on electricity or electric circuits, The Physics Classroom has a comprehensive free tutorial that features animations and question sets with answers. You can brush up your knowledge in a range of topics including electric potential, types of circuits, Ohm's Law and resistance, the meaning of "power", and more.  Click here:   http://www.physicsclassroom.com/class/circuits

Learning Objectives

NGSS

• Performance Expectations
  • 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.
  • MS-PS2-3. Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.
  • MS-PS3-2. Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.
  • MS-PS3-4. Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample.
  • MS-ETS1-3. Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.
• Disciplinary Core Ideas
  • Conservation of Energy and Energy Transfer
    • Light also transfers energy from place to place.
    • 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.
  • Definitions of Energy
    • Energy can be moved from place to place by moving objects or through sound, light, or electric currents.
    • The term "heat" as used in everyday language refers both to thermal energy (the motion of atoms or molecules within a substance) and the transfer of that thermal energy from one object to another. In science, heat is used only for this second meaning; it refers to the energy transferred due to the temperature difference between two objects.
    • A system of objects may also contain stored (potential) energy, depending on their relative positions.
    • Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present.
  • 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.
  • Types of Interactions
    • Electric and magnetic (electromagnetic) forces can be attractive or repulsive, and their sizes depend on the magnitudes of the charges, currents, or magnetic strengths involved and on the distances between the interacting objects.
• Practices
  • Analyzing and Interpreting Data
    • Analyze and interpret data to provide evidence for phenomena.
  • Constructing Explanations and Designing Solutions
    • Construct a scientific explanation based on valid and reliable evidence obtained from sources (including the students' own experiments) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.
  • Engaging in Argument from Evidence
    • Construct and present oral and written arguments supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon or a solution to a problem.
  • Planning and Carrying Out Investigations
    • Conduct an investigation to produce data to serve as the basis for evidence that meet the goals of an investigation.
  • Using Mathematics and Computational Thinking
    • Use mathematical representations to describe and/or support scientific conclusions and design solutions.
• Crosscutting Concepts
  • Energy and Matter
    • Energy can be transferred in various ways and between objects.
    • Energy may take different forms (e.g. energy in fields, thermal energy, energy of motion).
    • Within a natural or designed system, the transfer of energy drives the motion and/or cycling of matter.
  • Interdependence of Science, Engineering, and Technology
    • Knowledge of relevant scientific concepts and research findings is important in engineering.
  • Patterns
    • Graphs and charts can be used to identify patterns in data.
  • Science is a Human Endeavor
    • Advances in technology influence the progress of science and science has influenced advances in technology.
  • Structure and Function
    • Structures can be designed to serve particular functions by taking into account properties of different materials, and how materials can be shaped and used.
  • Systems and System Models
    • Systems may interact with other systems; they may have sub-systems and be a part of larger complex systems.

NSES

• Physical science - Transfer of energy
  • Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei and the nature of a chemical. Energy is transferred in many ways.
• Physical science - Transfer of energy
  • Electrical circuits provide a means of transferring electrical energy when heat, light, sound, and chemical changes are produced.
• Physical science - Transfer of energy
  • The sun is a major source of energy for changes on the earth's surface.

Discussion: Setting the Stage

Light Bulbs

• What are some different sources of light?

  Answers will vary, but may include light bulbs, fire, glow sticks, flashlights, and lanterns. Students may also mention the sun and the moon.

• Where does the energy come from to produce these types of light?

  Batteries: Chemical reactions within a battery cause electrons to build up. These electrons flow from the battery through the wires of a circuit, producing current. The chemical energy in the battery is converted to light energy. Electricity: Electrons flow through the circuit. Light that we see from the sun, stars, and moon come from different sources, the sun's light is produced during nuclear fusion (changing hydrogen to helium). The moon reflects the suns light.

Motion and Generators

• What is mechanical energy?

  Mechanical energy is the often defined in physics textbooks as "the ability to do work". This definition won't be very beneficial to students in this age bracket. It's better to discuss mechanical energy as the energy an object possesses due to its motion and position. It includes kinetic energy (energy of motion) and potential energy (often thought of energy of position).

Solar Cells

• How does a solar cell work?

  A solar cell is made of two layers of a silicon-based material. One layer has extra electrons (negatively charged) and the other layer has fewer electrons (positively charged). Light energy causes the electrons in the negatively charged layer to move around and flow to the positively charged side. When electrons flow, this produces an electrical current.

• What are some things that might make solar cells not work as a power source?

  If there are clouds or you are in a region that has limited sunlight during certain times of the year, they might not be a good energy choice.

Discussion: Formative Questions

Light Bulbs

• What components are needed to make an electrical circuit?

  Power source, conducting wires, device(ex. light bulb).  Teachers: A functioning circuit involves these fundamental components: 1) Source of electrical potential difference or voltage (battery or electrical outlet), 2) Conductive path that allows movement of charge (wires), and 3) Electrical resistance (light bulb, electric motor, heating element, etc.)

• Does the amount of heat produced continue to increase the longer the battery is connected?

  The amount of heat should eventually level off, though this might not be noticed depending on how long things are kept connected.

• Why do you think that you are measuring the heat that is being produced?

  Light and heat are both forms of energy, so by measuring heat you are measuring how much thermal energy is produced by the light bulb. Transformations of energy within a system usually result in some energy escaping into its surrounding environment. Some systems transfer less energy to their environment than others during these transformations, and we consider them to be more "energy efficient". As students perform this experiment, they will begin to get the connection between types of bulbs and efficiency. Incandescent bulbs are much less efficient than LED bulbs because their energy transformation produces more thermal energy that dissipates into the environment as heat.

Motors and Generators

• What are you measuring when you measure voltage?

  Voltage is a unit of electric charge. Voltage is the term used when describing the the electrical potential difference. This is different from concept of potential energy. The electric potential difference is the difference in electric potential (Volt) between the final and the initial location when work is done upon a charge to change its potential energy. Voltage can be a very difficult concept for students this age. Acceptable responses can range from "Volts measure charge" to "Voltage tells you how much electricity you have to work with."

• What happens when you turn the shaft on the motor?

  As the shaft spins, a coil of wire is rotated between the poles of two magnets. The magnetic field generates an electric current, and the electric current produces a magnetic field. The two motors you are using will have a magnetic attraction for each other, and you may test this by putting the motors side by side.

Solar Cells

• What is the purpose of the resistor?

  The purpose of the resistor is to regulate the flow of electricity within a circuit. Without the resistor, electrical surges may be enough to blow the bulb or other device connected to the circuit.

• Why do you use black paper to cover the solar cell?

  Black reflects the light so that its energy can't be used by the solar cell. These surges may be caused by lightning strikes in real life.

Discussion: Wrapping Up

Light Bulbs

• What are some factors to consider when choosing a light bulb? Explain.

  Answers will vary, but in general, students should include brightness required and efficiency desired.

Motors and Generators

• Describe the pathway of energy transfer as your finger turns the shaft on a motor and a bulb lights up.

  Mechanical energy from the fingers is transferred to the shaft. The turning shaft causes a coil of wire to spin between the poles of two magnets. This magnetic field produces an electric current. The electric current travels along the wires of the circuit and enters the bulb, causing the bulb to light.

Solar Cells

• The solar cells used to power homes and buildings are often very large and located on rooftops. Why are these factors important?

  Solar cells must be large enough to collect energy to run the intended devices. Open rooftop areas provide better access to sunlight needed by the solar cell.

• Why are solar cells made of dark materials?

  Darker materials absorb more light than lighter materials.

Additional Background

Electrical current is produced through the flow of electrons. The flow of electrons produces an electrical current, and an electrical current produces a magnetic field. Energy may be transferred throughout a system. For example, chemical reactions may be used to produce an electrical current that allows a bulb to light. A spinning coil of wire passing through poles of two magnets produces a current that is in turn transformed to make a light bulb light. During these processes, no energy is created or destroyed; the energy is simply transformed from one form to another. Through these processes, not all of the energy will be transformed to the desired product; i.e. light bulbs give off some energy as heat. The wires in a circuit may become hot and give off some energy as heat. More efficient means of energy production allow a greater portion of the energy produced to go to the desired product.

Analysis

Light Bulbs

1. Can electricity make heat but no light? What is your evidence?

   Yes. The paperclip heated up but no light was produced.

2. Compare the heating by a regular flashlight and the heating by an LED flashlight. Is there a large difference?

   Although the LED flashlight may produce some heat, it is generally less than a regular flashlight. LED flashlights are usually more efficient than regular flashlights.

3. Turn on the regular flashlight next to the LED flashlight. Which one is brighter?

   LED flashlights are usually brighter than regular flashlights.

4. If the flashlights are similar in brightness, the one with much greater increase in temperature is making more heat for the same amount of light. That means that much of the electrical energy is used up making heat instead of light. Based on your measurement, which type of light is more efficient?

   The light produced by an LED flashlight is generally more efficient than the light produced by a regular flashlight.

Motors and Generators

1. Can a motor be a generator? Explain.

   A motor can be a generator. The primary function of a motor is to change electrical energy into mechanical energy. In a DC motor, a coil of wire rotates between the poles of two magnets. The magnetic field produces an electric current and the electric current produces a magnetic field. In a battery-operated car, batteries give power to a motor that causes the wheels to turn. In turn, the generator converts mechanical energy into electrical energy to re-charge the car's batteries.

2. Can a generator be a motor? Explain.

   A generator can also act as a motor. The primary function of a generator is to change mechanical energy into electrical energy. An example is a battery-operated car. Batteries give power to a motor that causes the wheels to turn. In turn, the generator converts mechanical energy into electrical energy to re-charge the car's batteries.

3. Do you think some energy is wasted when you go from electrical energy to mechanical energy and back again? How can you tell?

   During energy transformations, not all energy from a source goes into the desired action. For example, with light bulbs some of the chemical energy from the battery is converted to heat energy as well as light. When going from electrical energy to mechanical energy and then back again, some of the energy will be transferred as heat energy.

4. Every gasoline-powered car has an electric starter motor attached to the gasoline engine. The electric motor is powered by the battery. When you start the car, the motor turns the gasoline engine over (rotates it) until it starts up. Is the motor acting as a motor or a generator? Explain.

   The motor is acting as a motor. Motors convert electrical energy into mechanical energy.

5. After the engine starts, the gasoline engine turns the motor, and the motor recharges the battery. In that situation is the motor acting as a motor or a generator? Explain.

   The motor is acting as a generator. Generators convert mechanical energy into electrical energy.

Solar Cells

1. How does the shading of part of a solar cell affect its voltage output?

   Shading part of the solar cell should produce less voltage.

2. How does distance from a light affect the solar cell's output?

   Greater distance between the light source and the solar cell should produce less voltage output.

3. How do you think distance affects output?

   Greater distance between the light source and the solar cell produces less voltage output. As the distance from a light source increases, intensity of the light decreases. This means there is less light to move the electrons in the solar cell, and less voltage is produced.

4. Can a single solar cell run a motor?

   Yes, a single solar cell can run a motor, but output may be limited. Solar buildings and houses require very large solar panels to generate a sufficient quantity of electricity.

5. Based on your experiments, would you say that solar cells are better for devices that require very little electrical energy or for devices that use more energy? Explain.

   The size of the solar cell determines how much light may be used to produce an electrical current. Larger (or more) solar cells can produce greater amounts of energy. Devices that require very little electrical energy require smaller or fewer solar cells.

6. How can solar energy be converted into electrical energy?

   Solar panels are made of two layers of silicon-based material. One layer has a negative charge (extra electrons) and the other layer has a positive charge (electron deficient). Light energy causes the extra electrons in the negative layer to move to the positively-charged layer. This results in electric current. The electrical energy is then converted into mechanical energy.

Further Investigation

Light Bulbs

Students may wish to measure the light output of regular flashlight bulbs compared to LED bulbs.

Many regions have considered limiting production and/or availability of incandescent light bulbs in favor of compact fluorescent light bulbs. What are some energy costs associated with incandescent bulbs compared to compact fluorescent bulbs?

Motors and Generators

Students may wish to research and construct a working water wheel and measure voltage output. Can water generate enough voltage to light an LED?

Solar Cells

Students may consider researching and constructing a solar-powered car. Some suggested materials include a solar phone charger and remote-controlled car.

Are some areas of the world better locations for solar energy? Students may wish to investigate the use of solar energy in different geographic regions.