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Applying a voltage to a material or device a current will flow through it, the current varies depending on the resistance of the material. Resistance is measured by ohms (Ω) and is the holding ability of a circuit or material to counter the flow of the current. Resistivity is a measure of the resisting power of a specified material to the flow of an electric current taking into account of its length and cross-sectional area this is measured by Ohms-metres (Ωm) the resistivity of Aluminium is varying from 2.65 to 2.82 × 10−8 Ω.
Ohms law deals with the relationship between voltage and current in an ideal conductor. This relationship states that: The potential difference (voltage) across an ideal conductor is proportional to the current through it.
Surface resistivity is the resistance to leakage current along the surface of an insulating material. Volume resistivity is the resistance to leakage current through the body of an insulating material. The higher the surface/volume resistivity, the lower the leakage current and the less conductive the material is.
Materials that are very resistant to the current are called insulators. Solids are classified as insulators, semi insulators and conductors by their static resistivity in the periodic table of elements. Static Resistance is the normal ohm resistance in accordance with Ohm\’s Law.
The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. Q=m c θ
Resistance is the electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it. R= v/I
Measurements in industry
Resistance and resistivity is measured with 2 or 4 wires, the most common method is the 2 wire method and is usually done with a multimeter with technology today they are getting more accurate
For more accurate results with a two-wire setup lab multimeters can measure the leads and the contacts within the circuit made. A four wire method is the way to measure the smallest of resistances the voltage is applied to two circuits this is referred to as the source circuit and the sense circuit.
Contact resistance now can be measured by measuring the same area as the test sample by the two wire probe and then a four wire probe after you subtract the differences the difference is equal to the contact resistance at the joint
Materials with high resistivity in industry
Carbon – this is produced by graphite or other types of carbon based compounds. Properties include high resistance to electrical conductivity (Diamond) but then graphite has a high electrical conductivity which is a carbon compound, carbon also has a high melting point and the highest thermal conductivity of all known materials (graphene)
Tungsten – tungsten is produced through a very complicated procedure from rare ores in the crust of the earth and acids (tungstics). The properties of tungsten are that it is very strong, very ductile and is very good at thermal conductivity, it also has a resistivity of 5.28 Ω.
Materials with a low resistivity
Silver – although being the best electrical conductors, other properties include high melting point, ductile also malleable and is also the best conductor of heat. Resistance for silver is 1.58Ω
Gold – although gold is very expensive you find in many of your electrical devices as it is very good at resisting corrosion and can last a very long time compared to copper. gold is very good a conducting electrical currents, gold has the highest malleability and ductility known to man and it also has a very high melting point. The resistivity of gold is 2.21Ω
(Ωm) Temperature Coefficient per Degree Conductivity
Silver 1.59 0.0038 6.29
Copper 1.68 0.00386 5.95
Aluminium 2.65 0.00429 3.77
Gold 2.21 0.0034 4.10
Iron 9.71 0.00651 1.03
It is a measuring instrument used to find the unknown value of electrical resistors below 1Ω, it is mainly used for resistors that are connected with 4 wires
Resistivity uses in industry
Resistivity is used in loads of things in industry from the oil/gas industry to the electronics and wires industry.
For the oil/gas industry they survey the surface with an electrical current this then acts like a virtual image that is relayed back to the equipment this is the most common way to find oil/gas in the earth\’s crust as the rocks show very high resistivity whereas the enclosed liquid does not it rather conducts the signal then the image is displayed with different colours and that shows if there is gas or oil in the crust. There is only one enclosed liquid that does not appear on the image and that is any hydrocarbon fluid as they are almost indefinitely resistive. So high resistivity values that are relayed back as well might show high amount of hydrocarbon liquid.
Resistivity can also help the industry in electronics where you need it all the time mainly lighting such as LEDs (Light-Emitting-Diodes) resistivity is needed as that you need to know the to know the maximal amount of current that is able to go through the diode as allowing the current to be too high would cause the diode to break as there would be too much current flowing through one direction, but it also works the same way too little current would cause the diode to not work properly so there needs to be an optimal balance in the current and resistance and this is where resistivity come in. This is also need for electrical products such as your laptop and computer as parts of the computer can break from too much charge.
Hazard Risk Possible Damage to Equipment Risk Rating Action Taken to Control Risk
Hot wire Being burned Wire, crocodile clips, ruler, tape Medium Do not get too close to the wire when on and give it time to cool down when off to make sure
Electricity Being shocked by the wire No damage to equipment Medium No contact with the wire. Also when not using the circuit turn it off by the plug to be extra safe
Fire/burning Being burned, damage to equipment Wire, ammeter, voltmeter, crocodile clips, ruler, tape, table surface High/Medium Do not leave the wire to overheat as it could melt and burn the table or start an electrical fire. The only way this could be a high risk is that when you get to the high resistance the wire could burn so recommending you get a partner for this part to make sure to give you the readings
- My hypothesis is as the wire length decreases, the resistivity decrease as there is less wire to go through.
- Equipment needed for the experiment
- We need constantan wire with a diameter of 0.27mm and 0.56mm
- Micrometer screw gauge
- 2 digital multimeters (voltmeter and ammeter)
- DC/AC Power supply (0-12V)
- Copper leads
- Crocodile clips
Set up the circuit to give you the right readings and have everything you need in the circuit
Choose the most appropriate potential difference as you don\’t want to break/burn the wire
Once you have the appropriate voltage start recording your results of potential difference and current
Once then recorded go down 10cm on the wire and record the measurements but making sure you take all health and safety precautions
Calculate the resistivity using the right equation
Then repeat this for the next wire
Calculations that are needed
In this experiment the resistance of the wire was calculated at the start to calculate the resistivity. The potential difference and current was calculated through the equipment we used (voltmeter and ammeter) this then helped to calculate the resistance of the wire.
Length Potential difference (V) Current (A)
1 metre 10.34 0.94
90cm 10.14 1.02
80cm 10.12 1.15
70cm 10.03 1.28
60cm 9.93 1.46
50cm 9.26 1.64
40cm 8.95 1.96
30cm 7.91 1.44
20cm 7.76 3.51
10cm 6.63 6.31
Test 1 Test 2 Test 3 Mean
11.00 11.20 11.23 11.34
9.94 9.86 9.88 9.87
8.80 8.68 8.82 8.76
7.82 7.63 7.80 7.75
6.80 6.59 6.84 6.74
5.64 5.50 5.89 5.67
4.56 4.40 4.83 4.59
3.24 3.46 3.66 3.45
2.21 2.34 2.70 2.43
1.05 1.25 1.45 1.25
This graph shows the mean resistivity
The results was as accurate as we could make them with the equipment we had, we did this by using 2 other results from students then found out the mean making the results as reliable as possible. With better equipment you could get more accurate results but is still accurate enough to see a possible correlation in the results. Finding the mean with all 3 results made the accuracy better as there was no anomalous results that was included keeping anomalous results can skew the results as it would look out of place. Other all the experiment was accurate and precise with the level that we are at and sets a good enough place to compare results.
In the graph it shows that as the length increases the resistance also does this was predicted in my hypothesis. To make the tests better we should have had a straight wire as it was hard getting the right length of the wire which could hurt the accuracy of the answers we got in the end you can see this in the tables where someone would be 0.2-0.3Ω out meaning this could of affected our results. The way we could of fixed this is by making sure you straighten the wire before using it and by putting tape at both ends to stop it from moving.
The only way we could of made the method more reliable and easy to recreate would be putting in more detail into it one way by doing this would be showing the diagram of the circuit so they know where everything would go. There is one human error that could of occurred and that is reading the results wrong on the ammeter and voltmeter as the numbers fluctuate around a number.
My hypothesis was unable to be disproved in any way my results correlated with the hypothesis saying as the length goes up so does the resistance of the wire. This was because electrons have to move along a longer circuit meaning there is more in the way of electrons also you are losing energy from heat lose.