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# Ohm's law.

Extracts from this document...

Introduction

## Ohm’s law

“Ohm’s Law states that the current through a metallic conductor at constant temperature is proportional to the potential difference. (p.d.). Thus p.d. over current is constant.” GCSE Text Book.

### What is resistance?

Resistance is defined as voltage over current. The unit of resistance is the ohm (Ω). So;

Resistance =

### Background Information  (Found in “Google.com”)

Electricity in wired circuits consists of the flow of electrons. Current is the word used to describe this flow, and is measured in amperes. Because positive and negative charge "dislike" being apart, current can only flow when a complete circuit exists: At least one closed loop for the electrons to run around.

Current flows because of an electric potential—voltage—that exists in the circuit. An example of a source of voltage is a battery; here electrochemical reactions produce electric potential. Another example is a power generator powered by steam (a turbine) or by rushing water (hydroelectric generators). The former are examples of constant (DC) voltage sources (most flashlight batteries produce a constant 1.5 volts) and the latter AC sources, where the voltage varies in a pattern like that of a sinus curve.

Circuits are comprised of the interconnection of circuit elements.

Middle

0.19

0.29

0.55

0.343

0.015

0.022

0.46

0.1656

10

0.7112

0.19

0.27

0.41

0.290

0.063

0.092

0.140

0.0990

20

0.7112

0.19

0.28

0.59

0.353

0.142

0.217

0.404

0.2543

30

0.7112

0.19

0.28

0.45

0.306

0.182

0.270

0.430

0.2940

40

0.7112

0.19

0.27

0.45

0.303

0.224

0.324

0.525

0.3570

50

0.7112

0.19

0.25

0.53

0.323

0.278

0.374

0.779

0.4770

60

0.7112

0.19

0.26

0.46

0.303

0.327

0.459

0.803

0.5290

70

0.7112

0.19

0.26

0.41

0.286

0.380

0.529

0.853

0.5870

80

0.7112

0.18

0.25

0.44

0.290

0.427

0.595

1.031

0.6843

90

0.7112

0.19

0.32

0.58

0.336

0.483

0.850

1.520

0.9510

100

0.7112

0.19

0.28

0.50

0.323

0.527

0.804

1.658

0.9960

For copper wire, swg 30

 Length(cm) Width(mm) Current Readings (Amps) Voltage Readings (Volts) Try 1 Try 2 Try 3 Ave. Try 1 Try 2 Try 3 Ave. 0 0.3150 0.21 0.33 3.58 1.5060 0.003 0.005 0.053 0.0210 10 0.3150 0.21 0.30 0.50 0.3366 0.007 0.010 0.017 0.0113 20 0.3150 0.21 0.43 2.90 1.1800 0.015 0.030 0.209 0.0846 30 0.3150 0.21 0.44 1.23 0.6260 0.020 0.038 0.107 0.5500 40 0.3150 0.21 0.47 2.11 0.9300 0.026 0.060 0.374 0.1530 50 0.3150 0.21 0.46 0.94 0.5532 0.027 0.060 0.135 0.7400 60 0.3150 0.20 0.39 1.80 0.7960 0.133 0.155 0.373 0.2203 70 0.3150 0.21 0.44 1.79 0.8130 0.038 0.080 0.326 0.1480 80 0.3150 0.21 0.39 0.70 0.4160 0.091 0.067 0.137 0.0983 90 0.3150 0.21 0.43 1.37 0.6700 0.056 0.114 0.380 0.2030 100 0.3150 0.21 0.37 0.91 0.4960 0.048 0.275 0.389 0.1840

For constantan wire, swg 30

 Length(cm) Width(mm) Current Readings (Amps) Voltage Readings (Volts) Try 1 Try 2 Try 3 Ave. Try 1 Try 2 Try 3 Ave. 0 0.3150 0.20 0.27 0.56 0.343 0.137 0.022 0.072 0.236 10 0.3150 0.20 0.30 0.99 0.496 0.015 0.185 0.386 0.363 20 0.3150 0.20 0.28 0.68 0.386 0.266 0.375 0.930 0.523 30 0.3150 0.20 0.27 0.61 0.360 0.379 0.542 1.213 0.711 40 0.3150 0.19 0.27 0.68 0.360 0.555 0.780 1.870 1.068 50 0.3150 0.19 0.26 0.58 0.343 0.644 0.910 1.997 1.1836 60 0.3150 0.19 0.30 0.41 0.300 0.731 1.201 1.161 1.0312 70 0.3150 0.19 0.30 0.81 0.430 0.830 1.374 3.710 1.971 80 0.3150 0.18 0.25 0.38 0.270 0.944 1.323 2.007 1.424 90 0.3150 0.18 0.23 0.34 0.250 1.026 1.358 1.960 1.448 100 0.3150 0.17 0.26 0.40 0.276 1.117 1.662 2.536 1.771

For manganane wire, swg 30

 Length(cm) Width(mm) Current Readings (Amps) Voltage Readings (Volts) Try 1 Try 2 Try 3 Ave. Try 1

Conclusion

Constantan is third,

And the least resistant is copper.

All the evidence her proves that my results agree with my hypothesis. (c.f. section P).

## Evaluation

### Reliability

The reliability of these results is quite good. This is because the procedure is relatively straight forward, and the numbers are not difficult to record. I think the results are certainly reliable enough to support both of my conclusions firmly.

### Anomalus results

There are a few anomalus results throughout the experiment. The resistance values in the table are not always increasing, and this is not always occurring at a steady rate.  Good example of which are the readings for 40 and 50 cm on the copper wire. I think that this is just a mistake in taking down the results or possibly we didn’t wait foe the voltmeter to stabilize.

### Experimental errors

These could include many things, the most likely of which are a short circuit,

The wire may have heated up causing less resistance, and the readings on the multimeters could have been inaccurate.

### Further work

This could include finding a more varied set of results, testing more types of wires. It could also include taking more readings to get better averages. I would suggest using all the rest of the equipment in the same way. Also one could try to investigate temperature changes by using insulated wires and a tray of cold/warm or hot water.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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