Copper, Constantan, Manganan and Nichrome

Conduction of electricity in metals requires a potential difference across two ends of a conductor for it to occur. This causes a flow of electrons in the wire, more commonly known as a current. The electrons in this current are free, meaning they are can move around in the wire freely. The number of free electrons depends on the wire. The more free electrons the better a conductor it will be. The electrons may however come up against some resistances while flowing in the current.

Resistance is the result of energy loss as heat. These resistances or obstacles, which slow the electrons down, are other electrons and the fixed particles of the metal i.e. atoms. These slow the electrons down because while they are flowing freely they collide with the other electrons and the fixed particles. These collisions convert some of the energy that the free electrons are carrying into heat.

The resistance of a length of wire is calculated by measuring the current in the circuit (in series) and the voltage across the wire (in parallel).

Then the resistance can be found by incorporating these values into this formula: –

R = V / I

Units

V = Potential Difference (Voltage) measured in volts

I = Current measured in amps

R = Resistance measured in ohms

It is also required to know of Ohm’s Law, which states that “The current through a metallic conductor is directly proportional to the voltage across its ends if the temperature or other conditions are constant.” This means that the resistance of a metallic conductor is constant providing that the temperature also remains constant.

Furthermore, as temperature increases the resistance of a metal also increases. This is because as the temperature increases, the particles gain more energy and are therefore moving around more quickly. This increases the chance of collisions with the electrons.

Prediction

I think that copper wire will be the best conductor. The copper wire I will be using is pure copper. Pure copper is used widespeadly in wiring, and surely it must have a low resistance for it to be used all over the world.

I think manganin wire will be the next best. It is an alloy containing 80% copper, 13 – 18% manganese and 1 – 4% nickel. This isn’t pure copper so it won’t be as good a conductor as the copper will be.

Constantan, which is also an alloy contains 60% copper and 40% nickel. This has less copper again therefore constanan will be a worse conductor than both pure copper and manganin.

Nichrome contains 20% chromium and 80% nickel. It has no copper in it so it will be the worst conductor of them all.

(I used the book “Tables of Physical and Chemical Constants” by Kaye and Laby to gather this information.)

In brief, I predict that the copper that is present in the piece of wire, the lower the resistance will be. The wire with the lowest resistance will be the best conductor.

Variables

These are anything, which can affect my investigation and results.

Independent Variables

These are variables that have to be changed. I will have to change the type of wire, which I am measuring the amperage from each time, to see which has the lowest resistance. I am using four different metal wires, these are: –

* Copper

* Nichrome

* Constantan

* Manganin

The voltage will also change because I will be setting it at different levels each time. The voltage will be measured in volts.

Dependant Variables

These are what I am going to measure in the investigation. During my investigation I will be measuring the ammeter. I chose to use it because it is a lot more accurate a digital meters, which was also available. The ammeter shows me the current in the wire and current is measured in amperes or amps for short. I will take at least five readings to ensure sufficient reliability.

Controlled Variables

These are what I am going to keep the same in the investigation. I will keep a number of things the same, things like: –

* Each of the four wires will have to have the same thickness and will have to be the same length (1 metre). I will also try and keep the temperature of the wire constant. I will do this by turning off the power pack when it isn’t being used so heat doesn’t build up in the wire.

* I will also have to use the same ammeter and voltmeter during the whole investigation because different meters may give slightly different results. I have to keep all these variables the same to ensure my investigation is a fair test.

Safety

* It is vital that I don’t set the power supply at too high a voltage as this could cause the bulb to blow. This would mean I would have to start and record all my results again. The bulb is in place to resist the current flowing in the wire.

* As I will be working with electricity, it is very important that I remember to turn off the power supply when I am changing over from one wire to the next. Failure to do this could cause the bulb or one of the meters to blow.

* I will have to try to take the readings as quickly as possible in case wire gets too hot. This would make decrease the accuracy of my results.

Apparatus

On this page I have listed all the apparatus I will use to make the circuit: –

* Power Supply

* Ammeter

* Voltmeter

* Bulb

* Wires

* 2 Crocodile Clips

* Length of chosen metal wire – Copper

– Constantan

– Manganin

– Nichrome

Diagram

I have drawn a diagram of the circuit I will use for the investigation: –

1 metre

Preliminary Work

In order to know the range of voltage and current I need to carry out some preliminary work. The voltages for each wire will be between 0V and 5V while all the currents will be from 0A to 1A.

This is a copy of the method I used to carry out my preliminary work: –

1. I set up the circuit I will use (shown on previous page)

2. For safety reasons, I started with the highest voltmeter and ammeter settings for each wire

3. I turned the power on and put it as high as I could without blowing the bulb

4. If this high current gave a reading that was low (it went off the scale) then I knew that the lower setting would be best for my experiment

5. I took the voltage readings and split them up into suitable ranges in order to give at least five readings

After doing the preliminary work I decided on the currents and voltages I will need for obtaining my evidence. They are as follows: –

Metal Wire

Current

Voltage

Copper

0A – 1A

0V – 1V

Constantan

0A – 1A

0V – 5V

Manganin

0A – 1A

0V – 5V

Nichrome

0A – 1A

0V – 5V

After finding out this information, I needed to split them up to find an actual scale for the voltage of each wire.

* For copper the scale will be from 0.02 to 0.10 going up in 0.02 volts each time.

* For constantan it will start at 0.5 and go to 2.5 going up in 0.5 volts.

* Manganin will go in 0.4 volts each time, ranging from 0.4 to 2.0.

* Finally nichromes voltage will go up 1 volt each time. It will start at 1 and go up to 5 volts.

Method

1. Take the first wire and set up circuit as shown in the diagram

2. Make sure the voltmeter and ammeter settings are the ones specified in the preliminary work

3. Turn on power supply at low output

4. Place the voltage at correct setting

5. Measure and record the current of the wire from the ammeter

6. Place the voltage at the next setting and again measure and record the current

7. Repeat until you have recorded 5 results

8. Change the wire and repeat steps 2 – 6 until you have got current for all four wires

9. Record all your results in a table and draw up graphs to calculate the resistances for each wire

Strategy for results

I am now going to draw a specimen table, which I will later use to record the results when I am obtaining my evidence. Then I will draw a specimen graph. This is a sketch of what I think my final graph will look like.

This is the table I will record my results in: –

Metal Wire

Potential Difference (volts)

Current (Amps)

I will use this table four times, once for each of the wires. Each time I will put in the name of the wire I will be using, and the appropriate scale for the Potential Difference.

On this page I have drawn my specimen graph

KEY:

= Nichrome

= Constantan

= Manganin

= Copper

Results

I have used the specimen table, which I constructed earlier to record my results.

Metal Wire

Potential Difference (volts)

Current (Amps)

Copper

0.02

0.1

0.04

0.18

0.06

0.28

0.08

0.38

0.10

0.45

Metal Wire

Potential Difference (volts)

Current (Amps)

Constantan

0.5

0.06

1.0

0.12

1.5

0.18

2.0

0.26

2.5

0.32

Metal Wire

Potential Difference (volts)

Current (Amps)

Manganin

0.4

0.08

0.8

0.16

1.2

0.24

1.6

0.32

2.0

0.40

Metal Wire

Potential Difference (volts)

Current (Amps)

Nichrome

1

0.05

2

0.10

3

0.16

4

0.22

5

0.26

On the next few pages I have drawn five graphs. Four of them show each wire individually and the fifth graph shows all four wires on it. From my graphs I will be able to find the resistances for each of the metal wires. To back up these results from my graph I will use the formula I mentioned earlier (R = V / I) and the results from my tables, to again find the resistances.

Resistances

Using my graphs, I joined the line of best fit as shown in the diagram below and then I was able to record the resistances: –

These are the resistances I found using my graph: –

Nichrome

Constantan

Manganin

Copper

A / B =

A / B =

A / B =

A / B =

4.8 / 0.2525 =

2.5 / 0.2975 =

2.0 / 0.4 =

0.0975 /0.45 =

19.01 ?

8.40 ?

5 ?

0.22 ?

I then used the information from my table and the formula, R = V / I, to see if the resistances matched up with what my graph results had said.

These are the resistances I found using the formula (R = V / I): –

Nichrome

Constantan

Manganin

Copper

20.00

8.33

5.00

0.20

20.00

8.33

5.00

0.22

18.75

9.38

5.00

0.21

18.18

7.69

5.00

0.21

19.23

7.81

5.00

0.21

Average =

19.23 ?

Average =

8.31 ?

Average =

5.00 ?

Average =

0.21 ?

Interpretation

The aim of my investigation was to find out which metal wire (copper, constantan, manganin or nichrome) was the best conductor of electricity. I predicted that the more copper that was present in the wire, the lower the resistance will be, the wire with the lowest resistance will be the best conductor. I thought that copper would be the best conductor as it had the lowest resistance, followed by manganin, then constantan and finally the worst conductor to be nichrome.

From my results I found out that as I had predicted copper was the best conductor. It had a resistance of 0.22 ? per metre, which was lower than constantan, resistance of 8.40 ? per metre, manganin, resistance of 5.00 ? per metre, and nichrome, which had a resistance of 19.01 ? per metre. This showed that the obvious trend was that the more copper the wire contains the lower its resistance will be. This also shows the prediction I made was correct.

I will compare my resistances from my graphs, and from my tables, to see if they match and to see if I notice any trends within them.

Metal

Table Resistance (?)

Graph Resistance (?)

Copper

0.21

0.22

Manganin

5.00

5.00

Constantan

8.31

8.40

Nichrome

19.23

19.01

The two results for each metal wire are all quite close together, the biggest difference being 0.22 ? in the nichrome. Due to this I feel confident enough that my results are reliable. This shows both my obtaining evidence and my graphs were accurate.

Copper was the best conductor because it had more free electrons. The electrons in the copper wire came up against fewer resistances while flowing in the current, than in the nichrome wire. Resistance is the result of energy loss as heat. These resistances or obstacles, which slow the electrons down in these wires, are other electrons and the fixed particles of the metal i.e. atoms. These slow the electrons down because while they are flowing freely they collide with the other electrons and the fixed particles. These collisions convert some of the energy that the free electrons are carrying into heat.

The following diagrams show this: –

Copper Wire:

There are fewer atoms so the electrons can flow more easily.

Nichrome Wire:

There are more atoms so the electrons find it a lot harder to flow.

I think the method I used for the obtaining evidence part of my investigation was fairly accurate and it allowed me to record my results suitably. I do feel that there are a few changes that I could have made. I should have firstly taken into consideration the wire fitting which joined the wire to the circuit. This metal fitting would add resistance to the circuit the circuit I was using because, electrons had to flow through it. Taking this into consideration I realise my results would have been slightly inaccurate.

Another problem I found was that the measurements for copper were very low and I found it hard to read off the voltmeter and ammeter. If I had used a new power supply which gives out the voltages more accurately then I would have got around the problem. Also using a less resistant bulb, it would have shared out the voltage more evenly. This would have also overcome this problem.

The results I got from my graphs were quite accurate but some slight anomalies did arise.

On my graph for Nichrome my line of best fit was quite accurate with only my second and fourth points only slightly off the line. From the book “Tables of Physical and Chemical Constants” by Kaye and Laby, the resistance value given was 13.9 ?. My result was 19.01 ?. This is not as close I feel I would have wanted it to be so I think that maybe due to some other reasons, which I have already mentioned my Nichrome results are slightly in accurate.

For my graph showing my results from the Constantan wire there were also some anomalies. The second and third points on the graph seemed perfect and went straight through the line of best fit but the other three points were quite a bit off it. Despite this my final resistance of 8.40 ? was quite accurate because the value given in the book was 6.3 ?. I was only 2 ? out this time compared to the nichrome when I was out by over 6 ?.

My results for manganin were the best by far. My line of best fit went straight through every point on the graph. I got a final resistance of 5.00 ?. Compared to the book this is again very accurate as the book says it should be 5.3 ?. I was only 0.3 ? out for this result. I didn’t have any anomalous results on the graph either. I was very satisfied with the result I got for manganin.

Finally copper. My results in the graph were again very accurate with only the last two points being slightly out. I feel a small alteration to my line of best fit would fix those two minor anomalies. The resistance I found the copper wire to be was 0.22 ?, which is a very small 0.028 ? of a difference with the book, which said the resistance for copper was 0.192 ?. Again I was pleased with my result and found it to be suitably accurate.

Overall I feel my copper and manganin results are very accurate while my results for constantan and nichrome are less accurate but still quite reliable as none of my results gave me any concern. Any anomalous results may have been because I read the equipment incorrectly or I left the bulb for too long and it heated up too much.

I think that my results support my prediction quite sufficiently because as I said in my prediction, copper would have the lowest resistance and therefore be the best conductor, followed by manganin, then constantan and that nichrome would be the worst conductor. My results show this so my prediction must have been suitably accurate.