Introduction: (Initial Observation)
So many devices and equipment around us are using electromagnetism as their driving force. Electric bells, buzzers, telephones, speakers, radios, and electric motors used in fans, hair dryers, vacuum cleaners and any other device that you can imagine are all using electromagnets.
This project is an opportunity to learn more about electromagnets and find out what factors affect the strength of an electromagnet.
Find out about electromagnetism. Read books, magazines or ask professionals who might know in order to learn about the electromagnet and it’s applications. Keep track of where you got your information from.
Following are some sample information related to electromagnet:
An electric current flowing through a wire produces a magnetic field. Coiling the wire produces a stronger magnetic field. Coiling it around a soft iron core increases the effect; raising the current or the number of coils increases it further. Electromagnets are based on this simple principle.
A basic electromagnet can be constructed around a long carriage bolt. Almost any iron core will work, including a large nail, but the bolt is simpler to work with. Screw a nut on to the end of the bolt so that there are two stops on either end, the nut and the head of the bolt itself. Wrap a piece of paper around the bolt between the nut and head and tape in place. Leaving a foot or so free, coil an insulated wire around the length of the bolt, between the head and the nut. Once the end is reached, coil the wire back to the other end. Repeat until there are several layers. The free ends of the wire should be at opposite ends of the bolt. Tape the wire so that it stays in place. Leaving a foot or so free, cut the wire off at the end. Strip the insulation off the ends of the wires. When the wires are attached to a battery (dry cell), the electric current around the wire and bolt will form a magnetic field. Don’t use it too long, as the battery will drain very quickly.
When constructing an electromagnet,
- It is best to use magnet wire, as it is thinner, and you can get more turns in a smaller space.
- The best core to use is soft iron. If cast iron or steel is used, it will be magnetized after the current ceases.
- The wire of the coil is usually separated from the core by a layer or two of paper, which serves as an insulator.
- The wire should be wound in smooth even layers.
- The outside diameter of the electromagnet should not be more than twice the diameter of the core.
- When winding a large coil, it will speed things along if you mount the core in a hand drill (unpowered).
A bit more elaborate setup is described in Experimental Electricity for Boys, by Willard Doan, 1959. This configuration acts more like a horseshoe magnet, giving the lifting strength of both poles at the same end. Keep in mind that this is from an older source, so some materials may need to be substituted.
“We need the following materials:
- two pieces of iron rod, 1 3/4 inches (44.5mm) long by 5/16 inch (8mm) diameter
- one bar of iron 2 3/4 inches (70mm) long, 1/2 inch (12.5mm) wide, 1/8 to 3/16 inch (3mm-4.75mm) thick
- four disks of fiber board or bakelite, 1 inch (25mm) diameter by 1/16 inch (1.5mm) thick
- 100 feet (30m) No. 23 enameled magnet wire
For the magnet cores, take two pieces of iron rod 1 3/4 inches long and 5/16 inch in diameter. They should be the softest iron possible. The unthreaded part of a carriage bolt of the right size will do very nicely. It may be softened further by annealing. that is, heated to a red heat and allowed to cool very slowly. At one end of each piece file a shoulder back 1/4 inch (6mm), reducing the diameter to 3/16 inch (4.75mm). This completes the cores (see Fig. 6-3).
To make the wire bobbins, cut four disks one inch (25mm) in diameter from fiber or other good insulating material about 1/16 inch (1.5mm) thick. Drill a hole in the center of each, slightly under 5/16 inch (8mm) in diameter, so it will make a tight fit when, forced on the core, using a vise. The assembled bobbin should look like Fig. 6-3. Two small holes should be drilled in each bobbin nearest the shouldered end of the core to allow the beginning and end of the wire to come through.
Wrap three or four layers of paper over the core for insulation.
Now we are ready for the winding of the coils. Wind each bobbin almost full of No. 23 or No. 24 insulated (preferably enameled) copper wire. This will require about 100 feet (30m) of No. 23 wire and slightly more if No. 24 is used. Wind each layer smoothly with the turns as close together as possible. Do not allow one turn to cross over another. Put a layer of paper, such as typewriter or thin wrapping paper, between each layer of wire. This makes it much easier m put on the wire and also acts as insulation between the layers. After the winding is completed, cover it with a protective wrapping of friction tape.
A yoke for the magnet coils may be made out of a bar of soft iron 1/8 or 3/16 inch (3mm-4.75mm) thick, 1/2 inch (6mm) wide, and about 2 3/4 inches (70mm) long. Drill a hole 3/16 inch (4.75mm) from each end for a mounting screw. Drill holes 1/2 inch (6mm) each side of the center in which the filed-down portion of the soft-iron cores will fit tightly. Insert the core ends, being sure the shoulders fit snugly against the yoke, and peen down the projecting ends to fasten the cores solidly to the yoke. Take a flat file and carefully dress down the outer ends of the cores so any flat object placed against the ends will fit perfectly against the surfaces of both cores.
Now with a compass as indicator and a dry cell for power, determine the coil connections. The coils must be connected in series so that one core will be a north pole at the end while the other core presents a south pole. Connecting the two inner ends of the coils together may give the desired effect or it may be necessary to connect an inner end to an outer end. The magnet should be used only intermittently on a single dry cell. Two dry cells may be used for a short period of time. If wound with No. 23 magnet wire and to the given dimensions, the completed magnet will have a resistance of approximately 2 ohms. With one dry cell this would draw a current of 3/4 ampere; with two dry cells, 1 1/2 amperes.”
A horseshoe effect can also be accomplished more simply, as in the following
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
Following are some sample questions about the factors that may affect the strength of an Electromagnet:
- How does the voltage affect the strength of an electromagnet?
- How does the number of coils affect the strength of an electromagnet?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
For the question number 1,
Voltage is an independent variable. Strength of electromagnet is the dependent variable. Number of coils, thickness of wire and the core are controlled variables.
For question number 2,
Number of coils is the independent variable. Strength of electromagnet is the dependent variable, Voltage, thickness of wire, and the core are the controlled variables.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following are sample hypothesis.
For the question number 1:
As voltage increases, the strength of electromagnet will also increase. (Exp. 2)
For question number 2:
As the number of coils increases, the strength of electromagnet will also increase.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1: (make an electromagnet)
Electric current creates a magnetic effect. This principle is used in creating an electromagnet. In this experiment you will make a simple electromagnet.
- an iron nail at least 2 inches long
- 3 feet of insulated copper wire, stripped at each end. (The gauge of the wire should be between 18 and 24. You can also experiment with different gauges.)
- 1.5 volt battery
- a box of small paper clips
Create an open circuit when you are not using the electromagnet. The wire gets hot from all the electron traffic. It can also drain your battery very quickly.
Do not experiment with any more than 6 volts and do not use anything other than flashlight batteries.
- Wind the wire about twenty times in a tight coil around the nail, leaving about a foot of wire free at either end.
- Connect one end of the wire to each of the battery’s terminals.
- Hold over the pile of paper clips.
- What happens? Why? (Electric current is now flowing from the battery into the wire, and a magnetic field is produced around the current. The nail is now an electromagnet. It will attract objects much as a bar magnet or horseshoe magnet would.)
- Make an open circuit. What happens? Why? (When you disconnect the wire from the battery, the nail loses its magnetic abilities.)
NOTE: Even after the current stops, the iron nail continues to be magnetized. To completely demagnetize it, strike it a few times on a table. Check to make sure it cannot pick up paperclips before you go on to the next experiment.
Things to think about and try:
- Determine how to measure and compare the strength of the electromagnet.
- Does the number of times the wire is wrapped around the nail impact how strong the electromagnet is? What is the magnetic power of a single coil wrapped around a nail? Of 10 turns of wire? Of 100 turns? Make predictions. Record the results held by the electromagnet.
- Is the strength of the electromagnet the same at either end?
- Does the shape make a difference? Try to make an electromagnet from a horseshoe. Wind the wire around one side of the magnet, then stretch it across to the other side and repeat. Connect to a battery as above. What happens? Why? (Since a horseshoe magnet has two poles near one another, both of which produce a magnetic effect, it has more strength than a similar-sized bar magnet would.)
- Does the core of the magnet make a difference? For
example, roll some aluminum foil in a tight roll and use it as the core for your magnet in place of a nail. What happens? What if you use a plastic core, like a pen?
- Does the type of wire you use make a difference?
(Magnetic wire, insulated copper wire.)
- Does the gauge of the wire make a difference?
- What difference does voltage make in the strength of an electromagnet? If you add another battery, does the strength of the electromagnet double?
- Can you find a way to make an electromagnet strong enough to lift a toy car?
- What is the heaviest object it can lift?
- Be careful not to confuse the earth’s magnetic poles with its geographic poles. The earth’s geographic North Pole is actually over one thousand miles from its magnetic north pole.
- Some metals are attracted to magnets — like iron, steel, cobalt and nickel. Other metals and alloys are not
- attracted to magnets — including brass, aluminum, tin, silver, copper, bronze, gold and stainless steel.
- “Tin” cans may be attracted to magnets — because they aren’t made of tin! They are usually made from steel coated with a thin layer of tin.
- Are American nickels attracted to magnets? No — because they are mostly made of copper. Try Canadian nickels for a different result!
- Why will magnets attract some straight pins and not
- others? Some straight pins are made of steel, which is
- attracted to magnets. Others are made of brass and coated with steel — magnets will not pick them up.
- Make sure that students understand that, in an investigation, only one factor should be changed at a time.
- Graph the results of the number of wraps, materials used for the core, and/or the number of batteries.
Experiment 2: The effect of voltage on the strength of an electromagnet.
Introduction: We can connect batteries in series to get higher voltage. In this experiment we test the strength of an electromagnet with 5 different voltages.
- Make an electromagnet with an Iron core such as nail or bolt and 100 turns of insulated wire on that (It is better if you use magnet wire).
- With a 1.5 volts battery in a closed circuit with the electromagnet, try to lift some small nails or iron filings. Weight the maximum amount of nails that the electromagnet can lift in 1.5 volts row of your results table.
- Then connect two 1.5 volts batteries in series with the electromagnet and try to lift some small nails or iron filings. Weight the maximum amount of nails that the electromagnet can lift. Weight the maximum amount of nails that the electromagnet can lift in 3 volts row of your results table.
- Repeat the above step with 3, 4 and 5 batteries in series and record the results in 4.5, 6 and 7.5-vlot rows of your results table.
- Repeat the above tests 3 times and record your results in your results table. Your results table may look like this:
Lift power or strength of electromagnet with different voltages.
|Voltage||Lift in try1||Lift in try 2||Lift in try 3||Average|
Add the numbers in each row and divide it by 3 to calculate the average. Write the average for each row in the last column of your results table.
Use the voltage column and the average strength column to draw a bar graph. You will have 5 vertical bars. Label the bars with voltages (1.5, 3, 4.5, 6, 7.5).
The height of each bar will show the average strength for one specific voltage.
Materials and Equipment:
List of material can be extracted from the experiment section.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
No calculation is required for this project.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
List of References
Additional Experiment (Optional): How to make an Electric Motor
Electric motors are among the most important devices that use electromagnet to work. In this experiment you will make a simple but working model of an electric motor.
Note: Make sure you try this experiment under the supervision of a teacher or parent.
- One ‘D’ Cell Alkaline Battery
- One Wide Rubber Band
- Two Large Paper Clips
- One Rectangular Ceramic Magnet
- Heavy Gauge Magnet Wire (the kind with red enamel insulation, not plastic coated)
- One Toilet Paper Tube
- Fine Sandpaper
- Optional: Glue, Small Block of Wood for Base
- Starting about 3 inches from the end of the wire, wrap it 7 times around the toilet paper tube. Remove the tube (you don’t need it any more). Cut the wire, leaving a 3 inch tail opposite the original starting point. Wrap the two tails around the coil so that the coil is held together and the two tails extend perpendicular to the coil. See illustration below:
Note: Be sure to center the two tails on either side of the coil. Balance is important. You might need to put a drop of glue where the tail meets the coil to prevent slipping.
- On one tail, use fine sandpaper to completely remove the insulation from the wire. Leave about 1/4″ of insulation on the end and where the wire meets to coil. On the other tail, lay the coil down flat and lightly sand off the insulation from the top half of the wire only. Again, leave 1/4″ of full insulation on the end and where the wire meets the coil.
- Bend the two paper clips into the following shape (needle-nosed pliers may be useful here):
- Use the rubber band to hold the loop ends (on the left in the above drawing) to the terminals of the “D” Cell battery:
- Stick the ceramic magnet on the side of the battery as shown:
- Place the coil in the cradle formed by the right ends of the paper clips. You may have to give it a gentle push to get it started, but it should begin to spin rapidly. If it doesn’t spin, check to make sure that all of the insulation has been remove d from the wire ends. If it spins erratically, make sure that the tails on the coil are centered on the sides of the coil. Note that the motor is “in phase” only when it is held horizontally (as shown in the drawing).
- For display, you will probably need to build a small cradle to hold the motor in the proper position. It might also help to bend the ends of the coil a bit so that as it slips right or left, the bends keep it in the proper position:
- Here is a diagram of the finished motor:
How It Works
When the un-insulated parts of the coil make contact with the paper clips, current flows through the coil, making it into an electromagnet. Since magnets attract, the coil attempts to align itself with the ceramic magnet. However, when the coil turns to face the magnet, contact is broken (because the insulation on one tail is now preventing current flow). Inertia causes the coil to continue around. When the coil makes are nearly complete spin, contact is re-established and the process repeats.
Technically (if you look up references on more complex motors), this motor is a single-pole pulse motor. More complex motors are created by using more than one coil and more complex set of brushes (the things that connect the coils to the current) so that no matter where the coil is in the spin pattern, at least one coil is always energized and trying to turn the coil assembly to align with the next magnet. This motor is, I believe, the simplest motor design which retains the basic concept of more complex motors.
Thanks to Chris Palmer for providing this experiment.