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Home , Electromagnetism

: and Motors Teacher Version

In this lab, we will see how and can be used together to create . Our source of electricity will be from a battery, and our source of magnetism will come from, of course, . With these two objects we will be able to create a motor, which will create motion in a piece of wire.

California Content Standards: • 5. Electric and Magnetic Phenomena: Electric and magnetic phenomena are related and have many practical applications. • 5e. Students know charged particles are sources of electrical fields and are subject to the of the electrical fields from other charges. • 5f. Students know magnetic materials and electric currents (moving electric charges) are sources of magnetic fields and are subject to forces arising from the magnetic fields of other sources. • 5g. Students know how to determine the direction of a magnetic produced by a current flowing in a straight wire or in a coil.

Prerequisites: • Better for older students (grades 8-12) • Requires assimilation of multiple concepts such as magnetism, insulation, electricity, etc.

Complete List of Material:

Part 1: • 3 steel/iron nails (3 different diameters) • 3 nine batteries (new batteries work • 10 feet of coated 24 gauge wire best) • paperclips • 9V battery connectors • 5 inches of string • sandpaper • scissors • 4 alligator cable clips

Part 2: • 24 gauge wire • 2 disk magnets (stronger magnets work • wire strippers or scissors better) • permanent marker • paper clips • or styrofoam cup • 2 large rubber bands • 2 alligator cable clips

Created by LABScI at Stanford 1 Key Concepts: • An is a negatively charged particle. • The flow of these negatively charged is called an . • When the flow in this current, they carry an electric , which causes electricity. This is the same electricity used to power many that you see everyday. Batteries are used to store electricity until you are ready to use it. • Electricity is closely related to magnetism. You are familiar with magnets. Motors work by using . This means that the magnetic part of something is turned on and off by using electricity. • Motors use electrical (from electricity) to create . In other words, motors are responsible for the movement of many devices including cars and computers. In fact, small motors and magnets are important parts of many kinds of medical equipment. Can you think of any other devices that use motors? • A conductor is an object that allows a charge to flow. Depending upon a material’s conductance, electricity can flow freely through the material. Metals are good conductors of electrical current. Another thing to consider when talking about electricity is resistance. • Resistance is the opposition of electron flow. Materials with a high resistance are not good conductors of electricity since they keep the current from forming. The wire is a good conductor, and the coating that protects it does so because it has high resistance. In order for the current to complete the circuit, it must be allowed to flow from the wire to the paperclip with little resistance. To do so, we must remove the insulation (what allows the resistance to occur).

Introductory Mini-lecture: All metals contain small magnetic fields in small regions of called domains, but their poles are all facing different directions so the small magnetic fields cancel each other out. It takes a lot energy to maintain a , so cancelling out the small fields requires less total energy. Certain metal such as iron or steel create stronger magnets because they are easier to align. When the iron is subjected to the magnetic field from the coil, the domains align based on the magnetic field of the coils (to understand the directionality of the magnetic field, see the right hand rule diagram at the end of the Teacher Version), and the combination of these small magnetic fields creates one stronger temporary magnet. This can be used for picking up household items such as a paperclip. In an industrial setting, using a lot more electricity, wire, and metal can create a magnet that can be used to pick up cars in a junkyard. In this experiment you will be seeing how the number of coils around a nail and the going through the coil can affect the strength of the magnet by seeing how many paper clips you can pick up while they are chained together.

Part 1 – Electromagnets In this part of the lab, we will see how an electric current can create a magnet out of normal metal objects. The metal objects that will be used are several different size iron nails, and the electricity will be provided by nine-volt batteries. The reason the nail becomes temporarily magnetic is because the electric current running in a helical shape creates a magnetic field. We will experiment with variations of the components of the electromagnets to see how changing the various elements will affect the power of the magnets.

Created by LABScI at Stanford 2

Effects of different amount of wires: 1. Wrap wire tightly around nail 10 times, leaving around 2 inches on each end. Remember to remove the insulation at the end of the wire using sandpaper or scissors. (See Figure 1) 2. Attach each end of the wire to battery using alligator clips. **WARNING: AFTER THE CIRCUIT IS COMPLETED, THE WIRES WILL GET HOT. 3. Straighten a paperclip. 4. On one end make a small loop that you can stick to the nail 5. On the other end make a little hook that you can tie the string to 6. Tie the string to the end of the hook and slide the paper clips over the string every two inches starting 2 inches away from the magnet. 7. Slowly pick the string up and count how many paper clips make it fully in the air before the paper clip attached to the magnet falls off. 8. Record number of paperclips on the chart below. 9. Change the number of wraps around the nail to 25, then 50. Make sure the first coil is the same distance from the flat nail head each time. 10. Record number of paperclips on the chart each time.

Number of wraps of wire Number of paperclips

25

50

Effects of different : 1. Wrap wire around nail 50 times. 2. Attach wire to 1 battery. 3. Slowly pick the string up and count how many paper clips make it fully in the air before the paper clip attached to the magnet falls off. 4. Record number of paperclips on the chart below. 5. Change the number of batteries to 2, and then 3, while keeping the number of loops around the nail the same (record number of paperclips on the chart each time).

Number of batteries Number of paperclips

1

2

3

Created by LABScI at Stanford 3 Effects of different sized nails: 1. Wrap wire around the smallest nail 50 times. 2. Attach wire to 1 battery. 3. Slowly pick the string up and count how many paper clips make it fully in the air before the paper clip attached to the magnet and falls off. 4. Record number of paperclips on a chart. 5. Repeat steps 1-4 for the medium and large sized nails. Make sure the first coil is the same distance from the flat nail head each time.

Nail Size Number of paperclips

Small

Medium

Large

Concept Questions:

Q1. Why do you use steel or iron nails? Steel or iron nails are used because it is easier for their domains to align than in some other metals.

Q2. Why do you use insulated wire as opposed to non-insulated wire? The electricity wants to find the shortest path possible so in non-insulated wire if the wires are touching the electricity will go straight across as opposed to going around the coil.

Q3. Based on the data for changing the number of coils, why would you want to have thin insulated wire instead of thick insulated wire? You want thin insulated wire because you are not working with high voltage so the wire insulation doesn't have to be as strong and with a thinner wire you can fit more coils around a smaller space which produces a stronger magnetic field.

Q4. Why do you think you hooked the paper clips to a string and held the magnet by one paperclip? You want to see how much weight it can hold instead of how far the mantic field reaches. With the paper clip on the string the paperclips are far enough away that the magnetic field isn't pulling the weight of each individual magnet but the weight of all of them combined.

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Created by LABScI at Stanford 5

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7. Clip one alligator clip to each of the paper clips and hook the other end to the battery.

**WARNING: AFTER THE CIRCUIT IS COMPLETED, THE WIRES WILL GET HOT

8. Give the coil a gentle spin; adjust the paper clips and coil until the coil spins continuously.

Different Testing Ideas:

How can we make our motor more powerful?

We can test your ideas on how to create a more powerful motor. We can increase the strength of the magnet we are using (use two magnets instead of one), vary how far we have the coil from the magnet, use a different type of wire (different resistance or conductivity), or change the number of coils we have in our wire. Which change makes the motor spin faster?

The insulated wire forces the electricity to pass through all the coils of the wire. As in the , this makes a temporary magnet out of the coils. It will be a magnet as long as electricity is flowing through the coils. If non-insulated wire is used, the electricity would take the shortest path open to it and would not go around and around the coils. /0 As in the other electromagnet, when an electron moves down a wire, it creates a weak magnetic field around the wire. By coiling the wire, we strengthen the magnetic field because we add up the effect of lots of electrons all moving around the coil in the same direction and all creating tiny fields. The more rounds of coiled wire, the stronger the field.

When this temporary magnetic field comes in contact with the magnetic field from the doughnut magnet, the attraction or repulsion is enough to push the thin wire coil around. The push/pull is just like bringing two doughnut magnets together... you can feel it! It's that alternating push/pull

Created by LABScI at Stanford 6 that keeps the motor going around and around. If you want to better understand the directionality of the push/pull you can look up the right hand rule for relating the direction of the magnetic field to the current through the wire (image below). If we want to make a more powerful motor, we can use more coils of wire (most industrial motors have hundreds) and stronger magnets.

Right Hand Rule: (image from Khan Academy)

Concept Questions:

Q5. An electromagnet is a magnet that runs on electricity. An electric current runs through an object (such as our wire) to produce a magnetic field. So, can you think of anything else in the motor that is magnetic beside the disk magnet we placed on top of the battery? The wire acts as an electromagnet. The electric current from the battery runs through the wire and produces a magnetic field within the wire.

Q6. An is a material that resists the flow of electric current. The insulation around the wire we used keeps the electricity within the wire. Do you think we needed to use insulated wire in order for our motor to work? Why or why not? Yes we do need an insulated wire in order for the motor to work. In order for our wire to act as an electromagnet, we need the electric current to remain within the coils of the wire. This creates a stronger magnetic field. The insulated wire forces the electricity to pass through all the coils of the wire.

Q7. Why do you think we coiled the wire? We coil the wire to create a stronger magnetic field. The electrons within the wire all move in the same direction, which creates a magnetic field. By coiling the wire, we can add up the effect of many electrons moving in the same direction each with its own magnet field.

Q8. Why did we scratch the coating off the ends of the wires that touch the paper clips? The insulation around the wire keeps the electric current inside the wire, and it keeps electric current from getting inside the wire. We scratched the coating off the ends of the

Created by LABScI at Stanford 7 wire to allow the electric current from the battery to flow through the wire.

Q9. What happens if we increase the voltage supplied by the battery (or replace the one battery with two batteries)? Increasing the voltage will cause an increase in current flow, which can be interpreted as an increase in power input. This will cause the motor to spin faster. In an ideal motor, the spin speed should increase proportionally to the increase in voltage. But due to non-ideal effects (internal resistances in the wires, back electromotive , ect) the spin speed will not quite increase proportionally to the increase in voltage.

Q10. What would happen if the area of the loop was increased? An increase in the area of the loop would theoretically not increase the spinning speed of the loop. This is because while increasing the area would increase the magnetic field produced by the coil making it spin faster, it would also increase the back-, which slows down the coil at the same rate.

Created by LABScI at Stanford 8