To investigate how electrical energy can be produced from a variety of energy sources and then transformed to almost any other form of energy.
This lesson is part of the Energy in a High-Tech World Project, which examines the science behind energy. Energy in a High-Tech World is developed by AAAS and funded by the American Petroleum Institute. For more lessons, activities, and interactives that take a closer look at the science behind energy, be sure to check out the Energy in a High-Tech World Project page.
This lesson will introduce electricity as the flow of electrons. In some cases, electricity can be the flow of positive charges or both positive and negative charges. This lesson will focus on the more typically defined flow of electrical current as that of electrons. Students should have some basic knowledge of atoms and their structure. However, as part of their online readings, students will investigate the basics of atomic structure (nucleus, protons, neutrons, electrons). Thus, this lesson provides a good opportunity to clarify misconceptions about atoms and to ensure that all students understand basic atomic structure. According to the Benchmarks for Science Literacy, students of all ages show a wide range of beliefs about the nature and behavior of particles. They lack an appreciation of the very small size of particles; attribute macroscopic properties to particles; believe there must be something in the space between particles; have difficulty in appreciating the intrinsic motion of particles in solids, liquids, and gases; and have problems in conceptualizing forces between particles. (Benchmarks for Science Literacy, (p. 337).) This misconception is important to keep in mind when talking about electricity as the flow of electrons. Students may think that the electrons are in the copper wire and not the copper atoms that make up the wire. It is important to stress this point with students so that they develop an understanding that substances are composed of atoms, rather than atoms residing as a separate entity within substances.
Electricity is the flow of charged electrons through a conductor (the cross section of a wire, for example). The flow of these free and moving charged electrons is referred to as electric current.
Electricity is generated from the conversion of primary energy sources, such as coal, oil, natural gas, nuclear power, and other natural sources. Burning or combustion of these primary energy sources provides energy in the form of heat, which is converted to the electrical energy that produces a current. Primary energy sources used to make electricity can be either renewable or nonrenewable.
Electricity—electric current—should be distinguished from voltage and from power. Electric current is the amount of electric charge which is flowing in a conductor, and is expressed as an amount of charge per amount of time. Power, on the other hand, is the rate at which energy is used, or the amount of energy expended, for a given unit of time. Electric power is the rate at which electrical energy is converted to or from another form of energy, such as heat or light.
The ratio of power to current is called the voltage. Voltage expresses the amount of energy expended per amount of electric charge.
Energy expended is determined by multiplying power by time. Thus energy can be measured by multiplying power expended in kilowatts by time in hours to get kilowatt-hours. Your electric meter does this automatically.
In the middle-school grades, students should be introduced to energy through energy transformations. Students should trace where energy comes from and moves next in examples that involve different forms of energy along the way: heat, work, light, motion of objects, position of objects, chemical, and elastically distorted materials. According to the Benchmarks for Science Literacy, in the early grade levels, there may be some confusion in students’ minds between energy and energy sources. Food, gasoline, and batteries are all sources of energy. When they are used, the energy they contain does not disappear; it is changed into other forms of energy. Similarly, their matter also changes form but does not disappear. In terms of where the energy goes, a sophisticated approach is one in which students realize that whenever some energy shows up in one place, some will be found to disappear from another. At this stage, students do not need to focus on the quantitative aspect of energy transformations. However, students should be able to trace the movement of energy as it transforms, and thereby notice that some is changed to heat and/or work.
Some resources will state that energy is “lost” to heat; however, the use of this term implies that we do not know where the energy is. It is clearer to talk about “change” rather than “loss” in energy transformations.
Work is a difficult concept. Work is done any time there is motion against some opposing force. For instance, when a block is pushed along a table, we must do work on the block to move it, and some of the energy we put into the effort is changed to heat due to friction. The work we put in, less the energy changed to heat, goes into making the block move—the block’s energy of motion.
Begin by showing students the pendulum. Pull the bob or mass of the pendulum to one side such that it is parallel to the table or ground. Hold it there. Ask students:
- Here at the top, does the bob have stored energy or motion energy?
(It has stored energy.)
- What is another name for this stored energy?
(Potential energy is another name for this stored energy. Potential energy comes from the position of the bob above the ground, against the earth’s gravity.)
(The energy is stored and the bob is not moving yet.)
- What will happen to the bob when I release it?
(The bob will start to swing back and forth.)
Release the bob.
- What happened to the potential energy of the bob?
(It was transformed into motion energy.)
- What’s another name for motion energy?
Grab the bob again to one side and hold it.
- What happened to the kinetic energy of the bob?
(It stopped because it is no longer moving.)
- What energy does the bob have now?
(It has potential energy.)
Hold the bob to one side but this time at a lower position (for example, at a 45 degree angle). Ask students:
- Does the bob still have potential energy?
- Does it have less or more potential energy than when it is held higher?
(The bob has less potential energy when it is lower than when it is higher off the ground.)
Tell students that the potential energy of an object can be more or less depending on its position. Provide them with other examples, such as a roller coaster or car starting to coast down a hill. Have them consider how potential energy affects how much kinetic energy will be generated when the object starts moving. For example, if the bob were released from a lower point, the kinetic energy generated would be less since there is less potential energy with which the bob is starting. This is also true of a car or roller coaster on a hill. The higher the position of the object on the hill, the greater its potential energy and the greater kinetic energy will be generated once it begins to move.
Reiterate to students that energy transformations can go back and forth. Potential energy can become kinetic and kinetic energy can become potential energy.
Now, ask students to imagine a vehicle, such as a car or a bus. Ask them: “How does the vehicle move?” Students may have a variety of answers such as “the accelerator,” or “the human that is driving it.” Encourage them until they say “gasoline.” Ask them:
- Why is the gasoline the thing that ultimately allows the car to move?
(If you press the accelerator of a car with an empty tank, it won’t move. If a human tries to start the car without any gas, it won’t start. Thus, gasoline is ultimately what is needed in the car.)
Tell students that gasoline is a chemical and is liquid. Ask them: “How does gasoline make a car move?” Encourage students to brainstorm and guide them towards the idea that gasoline is a form of energy that is transformed into kinetic energy or movement of the car.
When the gasoline burns, some of the chemical energy in the bonds that make up the gasoline’s molecules is released, creating a gas under pressure in the engine’s cylinders. When this gas expands, the pistons move. Another name for this energy is internal energy. Internal energy comes from the physical state of the gas in the engine’s cylinders.
Now, ask students:
- Is the gasoline or the moving car an example of moving energy?
(The moving car is an example of moving energy.)
- What is another name for moving energy?
(Kinetic energy is another name.)
Reiterate to students that internal energy is converted to kinetic energy.
In this part of the lesson, students will investigate how electrical energy can be produced from a variety of energy sources and then transformed into almost any other form of energy.
Plug in a small fan and turn it on. Ask students:
- Are the moving blades of this fan an example of potential or kinetic energy?
(They are an example of kinetic energy.)
(The blades are moving and the energy of motion is called kinetic energy.)
- Where did the blades get the energy to move?
(Students will mention that the fan was plugged into an outlet.)
- What type of energy is in the outlet?
(Electrical energy is in the outlet.)
- When we turn the fan on after it has been plugged into the outlet, what happens to the electrical energy?
(It is converted into kinetic energy by means of an electric motor. A motor works when an electric current passes through a wire in a magnetic field. The wire turns, and some of the electric energy is turned into kinetic energy.)
- What does the fan do?
(The fan’s blades move air around the room. The kinetic energy of the moving blades does work in moving air through the fan blades.)
- Is all of the electric energy expended in the fan turned into the work that moves the air? If not, what happens to the rest?
(It’s given off as heat. The fan converts electric energy into kinetic energy that does work, and it converts some electric energy into heat.)
Point to a light in the room. Ask students:
- What type of energy is coming from the bulb?
(Students should mention light energy. Some may also mention heat energy from their past experience with incandescent light bulbs.)
- A bulb on its own does not start to glow or release heat. So where is the light and heat energy coming from?
(Students should mention that electricity is used by the bulbs to generate light and heat energies.)
- What happens to the light and heat energy?
(It’s absorbed by the light bulb, and by the molecules of air into which it dissipates).
On the board, write out the following chart representing what is happening energetically with both the fan and the light:
Electrical energy (electricity) → kinetic energy
Electrical energy (electricity) → Light energy and heat energy
- In both cases, what is happening to the electrical energy?
(It is being transformed to other types of energy.)
- Where does electrical energy come from?
(Allow students time to brainstorm ideas about where electricity comes from. Some may mention that electricity is generated or that it is made in a power plant.)
Have students do the first part of the Transforming Energy student esheet using Forms of Energy. They can answer questions about this resource on the Transforming Energy student sheet. Answers to these questions can be found on the Transforming Energy teacher sheet.
Once students have worked through the resource, revisit the fan and the light that was mentioned in the Motivation. Ask students:
- Where did the kinetic energy of the fan’s blades come from?
(The electricity was converted into kinetic energy.)
- Electrical energy is a secondary source of energy. What does that mean?
(Electricity is generated from another energy source and is used to store and carry energy.)
- In the United States, where does most of our electricity come from?
(It comes from coal.)
- Is that a renewable or nonrenewable energy source?
(It is nonrenewable.)
- What does it mean to be a nonrenewable energy source?
(The energy source cannot be replaced and thus, it is available in limited supplies.)
- We have just learned that electricity is the flow of electrons. What is an electron?
(It is one of the basic structures of the atom, a negatively charged particle that travels around the nucleus.)
- What are some other structures that make up an atom?
(Protons and neutrons.)
Have students continue with the Transforming Energy esheet. After they have completed the esheet, show students the transparency of Electricity generation by conventional coal combustion. Using the answers from the student sheet, go over each step of electricity generation in coal power plants. Ask students the major types of energy being utilized and what energy transformations are taking place at each step.
To assess student understanding, ask them to use their student esheet to read and observe the How does electricity work? interactive. They should then answer the questions on their student sheet.
Ask students these four questions posed by the Heat, light and motion part of the Tech Museum of Innovation site:
- A toaster obviously converts electrical energy to heat energy. But what makes the toast pop up? (A timer is set by most toasters. Our energy pushes bread into a toaster, usually with springs. This energy is converted to potential energy in the springs. When the timer goes off, the springs pop up, in which potential energy is converted to kinetic energy and sound.)
- Most cars run on gasoline, but they also have batteries. What type of energy is a car battery? What types of things do you think a car battery is used to run in a car? (The battery is chemical energy. The chemical energy is converted into electric energy and the electric energy into light and heat energy for the headlights and sound for the radio.)
- Some ovens use electricity converted into heat energy to cook food. What kind of energy do non-electric ovens and stoves use? (Non-electric stoves and ovens use gas energy, a chemical energy. This is then transformed into heat.)
- What types of energy does a computer convert electricity into? (Light, sound, motion, and heat.)
The Science NetLinks lesson, Converting Energy, serves as an excellent introduction to this lesson plan.
A good follow-up activity from Science NetLinks is Power Play in which students examine energy transformations through the process of building virtual machines.
TESLA for Teachers, from PBS, offers a set of three lessons on energy appropriate for middle-school use. The first introduces potential energy. The second and third lessons use hands-on methods to show how mechanical energy can be converted to electrical energy and vice versa.
Have students investigate how electric vehicles work by going to A Student’s Guide to Alternative Fuel Vehicles. This will give them an understanding of how different types of energy, besides chemical energy in the form of petroleum, can be used to produce the kinetic energy needed to operate a vehicle.
Students can learn about the basics of circuits from Tech Topics: Electricity: Circuits.