What Affects the Strength of Magnetism Exerted By an Electromagnet?

Aim

I am going to investigate what factors affect the strength of magnetic field exerted by an electromagnet. I will use a number of theories to plan my investigation.

Iron, Cobalt or Nickel become magnetic when their domains point in the same direction. This is because all the N-poles add up at one end and the S-poles add up at the other end. These N-poles and S-poles then form concentrated magnetic areas relative to their direction. The will point towards ‘Magnetic North’.

This is the similar to what happens with lines of force. When any of the three magnetic metals become magnetic, they exert magnetic lines of force. These lines of force are called ‘Magnetic Fields’. These lines of force exeunt from the ‘North Pole’ and are attracted to the ‘South Pole’, or any other metal with magnetic capabilities.

We can demonstrate the ‘lines of flux’ (lines of force) by using a compass. A compass will follow the lines of flux from the North Pole. This is possible because the compass needle is magnetic with a North Pole and a South Pole. The North Pole of the needle is attracted along these lines of flux to the South Pole. This also demonstrates that ‘Unlike Poles Attract’. Like Poles (e.g. North and North) repel each other. This can be established by bringing two North Poles together. This can be achieved by magnetizing two pieces of metal, with magnetic capabilities, and cutting them in half. We result in two pairs of North and South Poles. Bringing the ‘Like’ poles together will result in the poles repelling each other. This method would be suitable because using two magnets with both poles could indicate that the opposite poles were attracting!

The Earth has a magnetic field. There are also poles named ‘Geographically’ North Pole and South Pole. The North Side of the compass needle will naturally point to the geographic North Pole. However, this would prove whole theory of magnetism incorrect. We have therefore decided that Magnetic South is Geographic North. Thus, the North Pole of a compass needle points ‘Geographic North’ and ‘Magnetic South’.

There are certain ‘Rules of Magnetism’ which have been founded. One of the most important is that:

Lines of force will never cross. This becomes evident when we sprinkle ‘Iron Filings’ around a magnet. The Iron Filings will lineup along the lines of flux. Using this demonstration, we can see that lines of flux don’t cross. This fact is directly linked with another rule. This rule states that there will always be a ‘Neutral Point’ between two repelling magnets. This is linked with the first rule because the lines of force won’t cross. Due to this, there will be an area between these magnets where there is no magnetic force. We call this region a ‘Neutral Area’.

How Is A Metal With Magnetic Capabilities Attracted?

Disregard of whatever material, magnets cannot attract metal without two sets of magnetic fields. As explained before, ‘Unlike Poles Attract’. This is because the lines of force which exeunt from the North Pole are attracted to a South Pole. Therefore, the magnets are attracted. Thus, no metal can be attracted by a magnet without its own magnetic field. However, In Magnesia (the origin of the discovery of magnetism), people found that magnets could attract metals which contained Iron, Nickel or Cobalt.

The explanation lies with the ‘Domain Theory’. By bringing a magnet near to one of the three mentioned metals, the domains of the metal line up repelling the North Pole of the Magnet. Thus, the metal core has magnetism induced into it from the current carrying wire. A South Pole will form nearest to the Magnet. The opposite side will therefore be a North Pole.

Now the metal has become magnetized, lines of flux exeunt from the North Pole of the metal and are attracted to the South Pole of the ‘Parent Magnet’. This procedure results in attraction.

However, the domains can be arranged using different methods. Bashing one of the metals with a hammer will distort the direction of the domains. There will become an uneven ratio of domains pointing in one specific direction. Therefore, a weak magnet can be formed.

Later on, ‘Hans Christian Oersted’ discovered that electricity has a magnetic effect. A wire carrying a current exerts a magnetic field. We can determine the direction by using the ‘Right-hand Grip Rule’. However, we could also determine the direction be looking down on top of the wire (90 degrees from the direction of the current). The direction of the lines of flux will go anti-clockwise.

Prediction

I predict that as the current increases through the wire, the current and voltage will affect the amount of magnetism induced into the iron core. This will inflict the alignment of domains on the ‘Soft-Iron Core’. Consequently, the Soft-Iron Core will become a stronger magnet with a larger magnetic field. This field will be capable of inflicting its magnetism (alignment of domains) on Cobalt, Nickel or Iron in range.

There should be a correlation between the current flowing through the wire and the magnetic field exerted and induced on foreign metal objects. I don’t think that as the current doubles, the magnetic force and field size doubles.

The strength of lines of flux is related to the number of aligned domains. However, I think that some domains are easier to align than others. This could be explained by the domains nearer to the outer surface of the core being easier to align than the domains located deep in the core’s matter.

The atoms of ...

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The atoms of metal near to the outside of the core, adjacent to the charge, might have a greater magnetic force inflicted on them. It is possible then that the number of domains aligned does not increase proportionally to the charge of the wire. This could be because as we progress deeper, there is less charge available (less charged electrons) to transfer from atom to atom as some of the charge is used up by traveling through the matter.

Where there is a concentration of charge, more domains could be aligned. Conversely, there must be areas of weak charge with insufficient energy to charge enough atoms to create an aligned domain.

This theory could be tested by inflicting magnetism on a core whilst placing a loud speaker near to the core. The intensity of the aligning domains could be recorded as loud speakers can pickup the aligning domains. This works because the magnet in the loudspeaker is affected by the aligning domains.

Hypothesis

I have made this prediction because as you increase the voltage and current, you will
induce more domains to line up- and if its proportional, you would then
double your current which would therefore double the domains (force).

Domains

If you were to cut a magnet in half, it doesn’t destroy the magnetism. In fact two
magnets will be created. However, if the magnet was cut exactly in between the poles, you would isolate each pole!

Supposedly, you could continue cutting a magnet in half, thus making the magnets smaller and smaller. In theory, if we used an extremely sharp, but still small blade, we would be able to continue cutting magnets in half until we reached a limit. This would be called a domain and is about 1/1000th mm long and would consist of about 10 thousand million atoms.

Using the current in the coils, I should be able to re-align some of the domains. This will result in more of the domains pointing in a certain direction. then the iron would I have made this prediction because as you increase the current, you will induce more domains to line up- and if its proportional, you would then double your current which would therefore double the domains (force). If you were to cut a magnet in half, it would not get destroyed. In actual fact, two magnets would be created.

If you wanted, you could continue cutting the magnets in half each time therefore making the magnets smaller and smaller. In theory, if we used an extremely sharp, but still small blade, we would be able to on cutting magnets in half until we reached a limit-this would be called a domain and is about 1/1000th mm long and would consist of about 10 thousand million atoms.

If you coiled a wire with a current around a Soft-Iron Core, you would be able to re-align some of the domains. This would inflict magnetism and consequently a magnetic field.

When you switch off the current, the domains will return back to a random set up. Obviously, if you were to line more domains up, the magnet would become much stronger, until you were to reach a state where you had aligned all the domains. It is at this point that you would reach the limit of magnetism for a mass of Cobalt, Nickel or Iron.

Why is a Magnetic Field produced due to the flow of a current?

Electric currents and magnetic fields are deeply related. An electron, or any other charged particle, placed in a magnetic field will move as a result that field inflicting its magnetism. If there are many of electrons, as in a conductor, they will all move and an electric current will be detected in the conductor. The reverse should also be true: - If a charged particle is moving then it produces a magnetic field.

The size of the magnetic field produced should be proportional to the charge of the particle. Bigger charges should produce bigger fields. However, the speed at which the charge is moving should also affect the field strength. The faster the particle vibrates, the more energy it has. Thus, a greater field is produced.

It must also be inversely proportional to ‘The Square of The Distance From The Charge’. This means that the field strength should get reduced as we move away from the charge. Fundamentally, a current produces a magnetic field due to the current consisting of many charges moving, each charge producing a magnetic field.

What is an ‘Electromagnet?’

An ‘Electromagnet’ is often a core of metal with magnetic capabilities (Iron, Cobalt or Nickel) in a coil of wire. When the wire has no current flowing through, the metal possesses no magnetic ability. However, when the current is passed through the wire, the core has magnetism induced into it. This is because the wire is adjacent to the metal core.

Apparatus and Planning

I based the majority of my apparatus and method on my computerized preliminary investigation. In this investigation I discovered that 3A (Three Amperes) is sufficient to gather relatively accurate results when performing the investigation on a small scale.

Paperclips Weighing 0.62g Each
Soft Iron Core Cylinder
Three Feet of Copper Wire
Mains Converter Outputs DC

It is vital that I used paperclips that were identical by size and mass. Therefore, to keep my investigation fair, I weighed each paperclip used and compared sizes. This was vital as the force of attraction is affected by the size of the paperclip. This is because if the lines of flux have a larger surface area to attract, the consequential induced magnetism will be greater according to my domain theory. The mass was also an important factor because paperclips are small; many domains deep into the paperclip’s matter will be aligned.

The optimal magnetism exerted from the electromagnet is affected by the number of charged coils of wire adjacent to a metal core’s surface. Therefore, by increasing the number of coils you will increase the magnetism exerted. You will also increase the strength by increasing the surface area of the core. The magnetism exerted by a specific mass of a core should be relatively proportional to the number of coils coiled around the core. I have chosen to use a cylinder core because of the large surface area. I need to ensure that the surface area of the core is kept identical throughout the investigation. To ensure the surface area is identical, I will need to leave short intervals of current inactivity. Although copper wires have a low resistance, heat is still produced after lengthy periods of electrical activity. This will enlarge the Soft Iron core resulting in an unfair test and producing inaccurate results. Furthermore, the magnetism exerted is affected by heat. Heating a magnet can distort the alignment of domains and demagnetize the core.

I am using a ‘Soft Iron Core’ because it instantly alters its exerted magnetism according to the current input. This is an important characteristic as the variable is the current flowing through the wire.

Three feet of charged copper wire should be capable of inflicting a significant magnetic force on the Soft Iron Core. Copper should be used because of its low resistance, thus limiting the heat output. The number of coils should be kept the same as it would affect the results and produce an unfair test.

The Mains Converter converts the 220 mains voltage into a safe sustainable voltage. It is important to keep a suitable distance between the electromagnet and the converter otherwise the electromagnet incorporated into the converter may tamper with the results.

Method

The method used has the ability to significantly affect the results gathered. Therefore the method requires in depth contemplating in order to achieve accurate and reliable results:

Paperclips are weighed and measured to ensure they are identical.
The wire is then coiled around the cylinder of Soft Iron and secured in place.
Crocodile clips attach to the coil of wire and attach to DC output terminals of the converter to ensure a good contact.
The converter is plugged into a mains socket and switched on with the output set to 0 Amps.
The paperclips are placed into a plastic cup so as they are arranged level and exactly perpendicular to the outside of the cup.
The electromagnet should then be brought into the cup until one of the poles just touches the top of the paperclips so direct contact is made.
The electromagnet is then slowly removed and the attracted paperclips are counted and recorded into a table.
This method is repeated for at variable currents increasing each time by 0.2 Amps unto a maximum of 3.0 Amps.
This entire set of results should then be repeated three times and averaged to ensure a suitable level of accuracy for the readings.

Overview

As explained earlier, I believe that the strength of an electromagnet varies according to the total voltage causing magnetic induction on the Soft Iron Core within a set time period. Using this information, two predictions were conducted:

The magnetic attraction exerted by an electromagnet will vary proportional to the voltage flowing within the coiled wire inducing magnetism into the core.

The magnetic attraction exerted by an electromagnet will vary proportional to the number of coils inducing magnetism into the Soft Iron Core.

Thus, by inducing magnetism from an electrically active wire into a Soft Iron Core, magnetic attraction is exerted. The strength of this magnetic exertion will increase as the induction from the wire increases. Subsequently, as the induction from a wire increases, so will the exerted magnetic strength. The strength is defined as the range of the effective magnetic field and the concentration of the lines of flux emitted.

However, the strength exerted will not be directly proportional to the coils of wire or the voltage. I believe that the magnetic strength emitted will be related to the voltage squared, as explained in my voltage theory.

Diagrams

Figure 2

Figure 3

Theories and How They Work…

The theory show above should apply to this investigation. The variable used is the current. Current is measured in ‘Amperes’. A transformer is used to scale down the standard British 240 mains voltage to an adjustable current. The transformer used proportions the voltage according to the current output. This is important as this would otherwise affect the results. A higher current to voltage ratio would loose energy because of excessive amounts of heat produced along the wire. This heat is produced when a high current passes through metal with a resistance. Copper wires are used to limit this resistance; however, some heat is still produced. This should not affect this investigation significantly, as if the voltage to current ratio is kept the same, the magnetism produced will still be proportional to the input current and voltage.

It is proven that the nearest section of a volume of metal being induced with magnetism will become a pole, opposite to the nearest source pole (shown in the diagram). The induced piece of metal will not equal the power of the source. This could be because not all the lines of flux result in contacting the metal. Thus, some of the power is always lost. These stray lines of flux will head either towards the sources opposite pole, any obstructing or nearby pieces of metal, or the ‘Earth’s Molten Metallic’ core.

Lines of flux are never directly transferred from piece of metal to another. In this case, the lines of flux induce magnetism into the nearest paperclips. These paperclips will then induce some of their magnetism into other nearby paperclips. Taking the above diagram and theory into consideration, the transferred magnetism form one paperclip to another will decrease as the distance increases. Therefore we can say that the amount of magnetic induction varies inversely to the distance from the source.

However, this does not mean to say that as long as the metal objects are equally very near/ touching, the paperclips will stay attracted to the source. There is still a limit. This is the amount of available induction. This induction is directly proportional to the voltage and current passing through the wire. Increasing the amount of induction available will increase the capable distance and number of contacting paperclips. Therefore, as mentioned before, more attracted paperclips should be expected as the voltage and current is increased.

Preliminary Data

A computer simulated preliminary investigation quickly identified the range of voltages that would enable accuracy in the primary investigation.

Figure 4

Figure 4 shows a clear correlation between the Voltage through the circuit and the Average Nails Attracted. Although it would seem that the number of aligned domains to applied voltage would decrease (see theories), the simulation only dealt with small voltages. Therefore, the electromagnetic field’s power is directly proportional to the voltage applied.

Figure 5

Although the results show direct proportion, the primary results will most defiantly show the electromagnetic power exerted decrease slightly as the voltage increases. This is a result of the power supply used, as the current will increase with voltage. The larger current will affect the resistance causing energy loss as heat in the wires.

Primary Data

The primary results were collected using the method shown in Figure 1. Four sets of data were collected to increase the reliability and accuracy of the data. These results could then be averaged to demonstrate a clear set of results.

The current was recorded as the power supply increases current with voltage accordingly. A transformer could have been used to ensure minimal energy loss of heat through the wires. However, recording the results in Amperes and not Volts ensures that the energy loss does not substantially affect the results.

Figure 6

Primary Results and Expectations

Figure 6 shows the results collected for the primary experiment. The number of wire coils was kept constant so as this factor would not tamper with the experiment.

Figure 7

The data collected in Figure 7 conclusively proves the hypothesis:

‘As the Voltage is increased, you will induce more domains to line up. This will consequently increase the influencing lines of flux and the power of magnetism.’

Putting this hypothesis into action through the experiment; more paperclips should be attracted and lifted against their weight as the voltage is increased. However, as the power supply increases the current with the voltage, there should not be direct proportion in the results collected. This is due to the increasing resistance opposing the increasing current. The energy loss will be given off as heat through the wires.

Figure 8

The experiment results should somewhat reflect this theoretical diagram.

Analysis of Results

Figure 9 shows how the number of paperclips attracted and lifter by the electromagnet varies as the current is adjusted. To avoid recording the result of resistance (shown in Figure 8), an Ammeter was placed in series to measure the resultant (affecting) current in the circuit. It is this resultant current that directly affects the magnetism induced into the soft iron core.

From examining the trend shown in Figure 9, it is clear that the hypothesis is true for this investigation on a wide range. It is visible that the resultant current of 3 Amps induces much more magnetism into the core than a lower 1.5 Amps. In addition, the results show proportionality. If this experiment was conducted on a larger scale with many repetitions, we could expect to see that the resultant current is directly and accurately influences the paperclips attracted.

However, some of the results attained in the investigation did not prove the hypothesis true. For example, the results for 1.2 and 1.4 amps attracted an equal 13 paperclips on average. This is shown in the graph by the line leveling in-between these two points. The same is also true for the 2.2 and 2.4 amp results.

The best explanation for these unusual results is reliability. The experiment was only repeated 4 times. By repeating the experiment many more times, we may see the results stray towards the line of best fit.

Degree Of Correlation

The degree of the correlation between two sets of data can be analyzed by using a Moment of Correlation Coefficient formula.

The formula is:

R= ∑ Xi Yi – nxy

√ (∑ Xi2 – nx2) (∑ Yi2 – ny2)

Where:-

Xi = Data Set 1

Yi = Data Set 2

X = Average of all Xi data

Y = Average of all Yi data

Firstly, I compiled a spreadsheet in excel to calculate the Correlation Coefficient using a computed formula. A perfect directly proportional correlation would produce the following:

Figure 9

It is visible in Figure 6 that the numbers entered increase proportionally to each other. Therefore, the correlation coefficient ‘R’ is calculated as 1.

Using the results from the rounded averages, I was able to calculate the correlation coefficient for the experiment.

Evaluation

Although some anomalies were apparent in the final averaged results, the experiment was conducted well using exactly the same apparatus. The anonymous results were influenced by many factors including position of coils, previous induced magnetism in the core and retained magnetism in the paperclips.

By looking at the results, it is obvious that the line attained from the results is greater than a line of direct proportion as the line curves slightly upwards. Using a soft iron core ensured that the magnetism was not retained in the core. However, the paperclips were made from steel that will retain the induced magnetism. Therefore, these paperclips will be attracted easily to the electromagnet as the experiment is repeated for each current.

This could have been prevented by replacing all of the paperclips in the container with paperclips that have scrambled domains and no retained magnetism.

A total of 100 coils were wrapped around the soft iron core. During the experiment it is possible for the coils to move. The movement of the coils can affect the number of domains aligned in the core, thus altering the power of the electromagnet. From this, numerous or single results can be affected.

The coils could be securely fixed and the electromagnet could be lowered by a vice to ensure the electromagnet is always lowered in the same position.

A soft iron core prevents the magnetism from the previous use to be retained. However, some magnetism can still be retained of the core is not hit against a surface or heated to randomize the domains.

This action was not used in the method and could have affected the overall results similarly to the retained magnetism in the paperclips.

Conclusion

Although there were a few faults in the methodology used in the experiment, the results attained display a correlation and agree with the hypothesis on a whole. The experiment could have been repeated to increase the reliability of the results, and the method could be changed to include the affecting factors stated in the evaluation.

Proportionality was shown in the results and the hypothesis was proved true. To conclude, the Resistance, Voltage and Coils around the soft iron core influence the attracting strength exerted by an electromagnet. Overall, the strength of an electromagnet is determined by the number of domains aligned in the core!

What Affects the Strength of Magnetism Exerted By an Electromagnet?