Реферат: What Is The Effect Of Increasing The

Current, On The Effectiveness Of An Electromagnet When Picking Essay, Research Paper



What is the effect of increasing the current, on the effectiveness of an electromagnet when picking up steel pins? Originally the idea was to count the pins that the electromagnet picked up, but this proved too difficult. Because of this, we decided to weigh the pins that had been attracted instead. Predictions

First of all, an electromagnet has to be defined. An electromagnet can also be called a Solenoid. An electromagnet can consist of just one wire, but usually an electromagnet is made up of wire coiled around a soft ferromagnetic core (a solenoid). This extract comes from the book ‘ The Working World of Physics’, ” Those like Iron, Nickel and Cobalt which are easily magnetised are called Ferromagnetic.” Materials that only react in a very strong magnetic field are called Paramagnetic. The picture below shows how Magnetic fields arrange themselves around wires carrying electricity. This picture comes from Encarta 97.

The above picture shows why an electromagnet works; the wires carrying electricity generate a magnetic field. We decided to use an iron nail because it is probably the best material available to use for a core and was really the only material available apart from steel. Materials that could also be used as cores include Steel, but these become permanent and are therefore useless in an electromagnet. According to the book, ‘The Working World of Physics’, Alnico and Ticonal, which are alloys of iron, nickel, aluminium and cobalt, could also be used but we did not use them for two reasons: They were not available.

They become permanent magnets so are therefore useless to use more than once without demagnetising them. I predict that as the current carried in the wire gets stronger, so will the magnetic field surrounding the electromagnet. Therefore, I predict that the amount of pins picked up will increase as the voltage gets higher until eventually the electromagnet can’t pick up any more pins (the point of magnetic saturation). Equipment


(to protect the surface of the bench)


(to hold the Electromagnet)

Clamp Stand

(to hold the Clamp)

Power Pack

(to control the voltage of the current)

Crocodile Clips

(to take the electricity to the Electromagnet)

Electromagnet: Iron Nail

(to act as a core)


(wrapped around the core) Method

Take the Iron nail and wind the wire around it, leaving the two ends of the wire free.

Clamp up the nail as below. Plug two crocodile clip leads into the Power pack and attach each crocodile clip to a different end of the wire which is wound around the nail.

Turn on the power to the required voltage and then bring the box of pins up so that the pins are touching the Iron nail.

If there are any pins still hanging, take them off and put them in the container.

Weigh the pins in the container.

The above method was repeated at 1, 2, 3, 4, 5, 6, 7 & 8 Volts. This experiment was a fair test because: The same power pack was used each time.

The same box of pins was used each time and the pins were all roughly the same weight.

Only one factor (i.e. the current) was changed.

The core of the electromagnet always had the same surface area.

The same equipment was used each time.

The pins were all made of the same material. Key Factors which could affect this experiment were: The metal that the core is made of.

The accuracy of the amount of electricity being used.

If the pins in the box are magnetised.

If the core stays a permanent magnet after the electricity is turned off.

If all the pins were made of the same metal. When using electricity, all components should be handled carefully. Results

It was necessary to repeat each result 3 times to confirm that each result was correct and not anomalous. Table Because 0 pins should be attracted at 0 volts, I added a data point for 0,0 on the graph. This makes the best fit line more accurate. The results showed in bold are anomalous because they do not fit in with the pattern that the other results follow. The experiment may not have been a completely fair test, as we observed that the iron nail would attract about 1-2 pins when the electricity was turned off. This meant that the nail did become slightly magnetised but only by a small amount. Graph

(Click on the graph to see an enlarged version of it.) Conclusion

The results did show that my predictions had been right. The amount of pins increased with increasing voltage, but the amount of pins started to stop increasing when the voltage was at 8 volts. This was probably because the electromagnet had almost reached the Magnetic Saturation point (i.e. it had almost attracted all that it could). The results also seemed to show a trend in the way they increased. Every time the voltage was increased by 1 volt, the amount picked up increased by roughly 2 grams. Probably the reason that some of the results were anomalous was because the voltage used wasn’t precisely accurate as the dials on the Power Packs can be misread slightly. Also, some of the pins may have become magnetised, or the nail may have become a weak permanent magnet. These reasons could also account for the spread of data in the other results. My best fit line didn’t pass through the origin, although it came very close. This is probably because the iron nail which was used as a core was slightly magnetised and therefore acted as a weak permanent magnet, before the electricity was turned on. Generally, my results are confirmed in the book ‘Explaining Physics’:

On page 289 of the book ‘Explaining Physics’, it says, “Experiments show that, for a solenoid of any given length, the strength of the magnetic field can be increased by increasing the current.” The fact that the electromagnet gets stronger or weaker as you change the voltage is a useful one. This is because in the ear-piece of a telephone, different strengths of current go through an electromagnet which moves an iron disk. The stronger the current, the further the disk moves. The disk creates sound waves which you hear when you listen to someone on the telephone.

The book ‘Physics for you 2′ says, “As the currents vary, the movement of the disk varies and makes a sound wave in the ear. Improvements

If this experiment was used again, I would try to improve it in the following ways: Using Iron filings or something that would give a more accurate weight.

Taking more readings at different voltages.

Using a material for a core which won’t become a permanent magnet when the electricity is turned off.

Taking more readings at higher voltages to try and get to the point of magnetic saturation. References – Books

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