Materials Included In Kit

Additional Materials Required

Prelab Preparation

Cut the sandpaper into eight pieces to distribute to the lab groups.

Safety Precautions

Exercise caution working with neodymium magnets—they are very powerful and will snap together easily. Have students wear gloves to protect their fingers. The magnets are fragile and may shatter if dropped or if they hit another object too hard. Keep magnets away from electronic devices. Remind students to wash hands thoroughly with soap and water before leaving the laboratory.

Disposal

All materials may be saved and stored for future use. Do not store magnets near electronic devices.

Teacher Tips

• A complete circuit is essential for success in this laboratory activity. If a voltage drop over the wire is not produced, the LED will not light. Students will need to verify that the ends of the wires are well sanded and not touching each other to ensure good conductivity.
• Although the magnets will introduce a resistance force when spinning the nail, it should still not be difficult to spin. If it is, students should wiggle the nail through each individual hole to make it easier.
• A greater number of turns of wire can increase the generator’s output. Have students test the generator with more or fewer turns.
• If students cut the wire too short, and the generator does not light the LED due to lack of coils, have them sand the ends of the coiled wire and the wire spool, and twist them together. Have them test the edges of the shaved region to make sure they have a circuit through the twisted wires, and continue spooling.
• Keep neodymium magnets away from computer disks or other magnetic strips such as credit cards. They will quickly erase the magnetized data.
• LEDs will burn out easily with too much current, and are thus usually connected in series with a resistor. Connect the generator to a multimeter set to measure alternating current and ensure the current does not exceed 30 mA, the maximum current a typical LED can take.

Sample Data

Observations

The LED flickers because LEDs only light when current is flowing in one direction. The current produced is alternating directions, therefore the LED will only light when the current is going the correct way.

Answers to Questions

1. What are the components needed to make a generator?

   Conducting coils of wire, a strong magnetic field, and some method of changing the field with respect to the coils are needed to make a generator.

2. In your own words, describe how the generator creates power.

   As the magnetic poles are spinning around, the field they generate spins with them. Because the coils of wire are stationary, this means the field going through them changes, creating a changing magnetic flux. A changing magnetic flux produces an electric current in the wires, which lights the LED.

3. What are some sources of mechanical power that are used to generate electricity in generators in power plants?

   Mechanical power may be generated by spinning wind turbines, water wheels, and water dams.

4. How do thermal power plants, which generate heat by burning fuel or some other method, generate electricity?

   Thermal power plants generate heat to boil water, which creates steam. The steam then spins turbines, which spin generator rotors, producing electricity.

Introduction

How do you create electrical energy from mechanical energy? Build a simple generator that will light an LED when the device is spun.

Concepts

• Electric generators
• Alternating current
• Electromagnetism
• Faraday’s law

Background

A generator is a device used to convert mechanical energy into electrical energy. The source of the mechanical energy can be many things—a windmill, a water wheel and even a human being. A generator operates in the opposite manner of an electric motor, which converts electrical energy into mechanical energy. In fact, the two devices can be used interchangeably. Providing mechanical energy to a motor by spinning its shaft will cause it to produce electrical energy and providing electrical power to a generator will make the shaft spin. However, the designs of a generator and motor are typically such that it’s more efficient to convert energy in one direction only.

The key to both generators and motors is the interactions between electricity and magnetism, or electromagnetism. Although scientists had earlier noticed similarities between electricity and magnetism, it wasn’t until 1819 that Hans Christian Oersted (1777–1851) observed a physical connection between the two. While lecturing on electrical circuits, he connected a circuit near a compass. To his surprise, the compass needle was deflected when current was flowing through the circuit. Oersted had discovered that a current-carrying wire produces a magnetic field (see Figure 1).

Oersted’s discovery helped scientists understand how electricity could induce magnetism, but it took a few years more to understand how magnetism could generate electricity. In 1831, Michael Faraday (1791–1867) discovered through careful experimentation that “any change in the magnetic environment of a coil of wire will cause a voltage to be ‘induced’ in the coil.” This is known as Faraday’s Law—a changing magnetic field produces a voltage called electromotive force, or emf. A changing magnetic environment—spinning magnets—induces a voltage in the coils. When voltage is induced, electrons flow through the wire. The amount of voltage or emf induced depends on the strength of the magnetic field, the number of wire coils, and the speed at which the wire or magnet is moving.

Generators today usually contain a large, stationary permanent magnet, called the stator, and a moving coil of wire, called the armature. The mechanism to rotate the coil of wire in the magnetic field is called the rotor. In this activity, a simple AC generator will be built using the rotating magnet. As the magnet rotates, the direction of the magnetic field will change, which will change the magnetic flux as well.

A mathematical description of Faraday’s Law is shown in Equation 1. where

Emf is the electromotive force or voltage (V)
N is the number of turns in a coil of wire
ΔΦ is the change in magnetic flux
Δt is the change in time

Magnetic flux (Φ) is defined as the average magnetic field multiplied by the perpendicular area it penetrates. The equation is: where

B is the magnetic field
A is the perpendicular area

Faraday’s law shows that the greater the change in flux occurring, the larger the voltage. Using this, Faraday was able to create the first simple generator, a design similar to the one employed in this activity. This meant that instead of creating voltaic cells—batteries—using expensive chemicals, current could be produced continuously, provided one had a constant source of spinning motion. The stronger the magnet, the more turns in the coil and the faster the magnets can be spun are all directly related to how much voltage a generator will produce. The magnets used in this activity are made with neodymium, a rare earth element and are some of the strongest permanent magnets available conventionally.

Materials

Safety Precautions

Exercise caution working with neodymium magnets—they are very powerful and will snap together easily. Wear gloves to protect your fingers during the preparation. The magnets are fragile and may shatter if dropped or if they hit another object too hard. Keep magnets away from electronic devices especially computers. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Procedure

Prparation

1. Measure the length of the cardboard tube and mark the center.
2. Push the tip of the nail through the cardboard tube at the center mark and drop the nail straight down. Poke a hole through the other side as well.
3. Make a short (0.5 cm) diagonal cut at the top of the tube to hold the wire.
4. Unwind a small length from the coil of magnet wire (about 10 cm), and hook it into the cut (see Figure 2).
   {12738_Procedure_Figure_2}
5. Wind the wire around the cardboard tube at least 300 times. Be cautious to not pull too tightly, as the thin wire may snap. Note: The more coils, the easier it will be to light the LED.
6. Once you have the desired length, spool a bit of excess and cut the wire. Note: Skip this step if you intend to vary the number of turns.
7. Make another diagonal cut on the opposite end of the cardboard-tube generator and secure the wire end in it.
8. Use the sandpaper to remove the enameled coating on the two ends of the wire coiled around the generator.
9. (Optional) Test the coil using the multimeter’s “continuity beeper” function to ensure you have a complete circuit. If the test indicates you do not have a complete circuit, remove more enamel from the ends of the wire. Check the resistance to ensure the total resistance is less than 100 Ω.
10. If necessary, widen each hole again by inserting the nail through one hole at a time and then wiggle the nail using circular motions until the nail can spin easily.
11. Test the nail’s ability to spin by holding the nail steady and spinning the cardboard tube. The tube should spin easily, without much friction to slow it down. If not, repeat step 10. Leave the nail in its slots (see Figure 3).
    {12738_Procedure_Figure_3}

Activity

12. Carefully detach the magnets from each other. Slowly bring one inside the generator, gripping it loosely so it will attach to the nail on its own. It should attach by the circular end (one of its poles).
13. Reach in with your fingers and grip the magnet attached to the nail to hold it in place. Grasp the other magnet firmly, and slowly and carefully insert it into the other end of the tube. If opposite poles are facing each other, a pulling force will be felt. If a force of repulsion is felt, flip the magnet around. Gripping both magnets firmly, bring the second magnet as close as possible before releasing it, allowing it to attach to the other side of the nail (see Figure 4).
    {12738_Procedure_Figure_4}
14. Wind each shaved end of the wire around the wire leads of the LED, ensuring that the two leads do not touch each other (see Figure 5).
    {12738_Procedure_Figure_5}
15. Spin the nail with both hands. Increase the spinning speed until you can see the LED flicker on and off (see Figure 5).

Student Worksheet PDF

12738_Student1.pdf