Physics investigation- Strength of Electromagnet

Method

During our preliminary work we found it would be best in the experiment to change the current in steps of 0.5 amps this will happen from 0 amps – 4 amps. To vary the current will keep the voltage output from the power pack at 13 volts and then using a variable resistor to adjust the current. To measure the current we will use an ammeter. The electromagnet will be 5mm from the scales and magnet as we found in the preliminary investigation that 2cm was too far away to have any effect and less than 5mm would attract the magnet too quickly. We will place the magnet on the scales so that it is opposite to the electromagnet in poles. We will measure the weight of the electromagnet without the circuit being on. We will then begin at 0 amps (which will have no effect) and then follow with 0.5 amps, 1 amp up to 4 amps. Each step measuring the mass of the magnet n the tip from balance, as the current increases the mass of the magnet will also decrease.

        With the measurements of the weight we will find an average increase and use it in the formula to find the overall force:

        

1. Collect equipment.
2. Set up as per diagram
3. Wrap coils around iron core 90 times; make sure that the tip of each end is uncovered so that the crocodile clips can touch the wire.
4. Cello tape magnet to balance so that it won’t move.
5. Adjust the electromagnet so that it is 5mm from magnet that is upon balance
6. Connect circuit turn the power pack on at 13 volts.
7. Adjust the amps to 0.5 amps
8. Record difference in mass.
9. Repeat in steps of 0.5 amps up to 4 amps using the variable resistor and ammeter, each time recording the mass.
10. Turn off.
11. Repeat experiment a further 2 times

Safety

Do not exceed the current of 4 amps, as the variable resistor will over heat. Make sure that no wires are uncovered; although the current is probably too small to give a shock there is no reason to take a risk. The use of a safety pack means another fuse. The power pack also has a reset button which pops out when the current is too great. We found from the preliminary work that it is safer if after every recording we will turn the circuit off at the power pack so that the variable resistor has chance to cool down and prevent any chance of over heating. Using a low voltage power pack meant that there was no way of us exceeding 13 volts thus not giving out a high enough voltage for any one to receive an electric shock.

Analysis

I found that as I increased the current the strength of the magnet increased. This agrees with my Hypothesis in the way that an increase in current meant that more domains of the atoms were facing in the same direction. Unfortunately 4 amps (our maximum output) and 90 coils wasn’t enough to reach a point of saturation. If we did, it would have been shown as a straight flat line on the graph. This then means we could not prove the hypothesis but support it, to prove it we would need to increase the current and have more coils. In our graph we can see what may be the beginning of saturation with the last few results but we didn’t have very reliable results for the points from 3.00 to 4.00 amps, more investigation is need to find out where they should be plotted. The final point (4amps) is anomalous as it doesn’t fit the trend we expected I have circled this with blue ink instead we used the on individual result (circled in red) which shows the expected results. One reason why the results were different is because of a anomalous result that being 13.2 this result unsettle the average

Limits

• A maximum 0f 4 amps stopping us reaching a point of saturation
• A maximum number of coils
• Only repeated the test twice
• We had to settle for the nearest amps to the round figures we wanted

 

Why?

‘Stephen Pople’s co-ordinated science’ book supports what I found out, on pages 152-153, it mentions that an electromagnet becomes saturated after so many coils have been wrap around the iron core. It tells us that an unmagnitised piece of iron has its domains spread out and angled in different directions

 When we increased the coils around the iron core, more and more Domains faced in the same direction until eventually they all did, and the magnet became saturated as no more domains could face in the direction therefore the strength could not increase

Evaluation

The investigation met our aim, as it is sure that the strength of an electromagnet is increased by an increase in current and in the amount of coils. Our plan needed some adjustments:

• We needed to increase to the current further to see a point of saturation.
• The electromagnet picked up the magnet in test 2
• To stop this we could have increased the distance of the electromagnet from the scales or change it so that the poles were opposite and the weight increased this is because the electromagnet would push down on the magnet.

  Our results seemed to be accurate bar one result (13.2 in the 4amps row) We can see that the result is anomalous as it is very different to the other result, I am sure that the other results wasn’t the anomaly as it fitted in with the trend we would expect to see. The reason for the anomalous result may have been after the electromagnet was turned off (to give the variable resistor chance to cool down) the magnet may have retained some of the magnet strength meaning when it was turned back on the strength was more than expected. We needed more time so that we can repeat the experiments more times giving a fairer average i.e. with the 4.00 amps point we had two results 13.2 and 10.1 there is quite a difference between these results which means the average has to be in the middle, it was 11.6 if the 13.2 result was more like we expected e.g. 10.5 then the average would be 10.3 fitting the trend and helping to prove the hypothesis.

Reasons

• Difficulty to have it on exact amp we may have had to settle for 0.97 instead of 1.00
• The strength in the magnet was sometimes retained from the previous reading
• The scales may not have been accurate. I know we had trouble to get the scales to know that nothing was on there it thought that there was a weight of 0.2 grams upon it.
• In the second test the electro magnet picked up the other magnet as the strength was too strong this was probably because the magnet retained some of its strength

 We need to investigate the points from 3.00 – 4.00 amps as this is not as we expected but the rest of the results prove part of the hypothesis but not the saturation part

Improvements

• To stop any chance of the electromagnet attracting the magnet it would be better to change the side of the magnet so that they are repelling and pushing down on the scales and then we would use the formula again to find the force. We know that when a magnet goes near another metal it induces the metal which is why it attracts it, but as we used a magnet for the electromagnet to attract we have to be sure that the magnets same ends are facing each other, other wise they won’t repel each other.
• Investigate the 3.00 – 4.00 amps part
• Repeat the test to give a fairer average
• Use more coils to help try and find a saturation point 150 would be sufficient
• Use a second Iron core

I would do the experiment again with the improvements so that we would see a point of saturation. Adjusting the current using a variable resistor and ammeter in steps of 0.5 amps from 0 – 4. With the increase in coils the strength of the magnet would have increased so 4 amps should be enough to see the domains of the magnet become saturated.