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Resistance Investigation: Essay, Research Paper

Physics Investigation Of Resistance Aim: to investigate how the electrical resistance of a wire changes in relationship to it´s length. Prediction: I think that as the length of the wire increases so to will the resistance of it. I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length. The graph to show this should therefore look something like this:Reason: with electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. All metals are conductors and have an arrangement in similar form to this:

As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. Resistance is encountered when the charged particles that make up the current collide with other fixed particles in the material. As the resistance of a material increases so to must the force required to drive the same amount of current. In fact resistance, in ohms(R) is equal to the electromotive force or potential difference, in volts (V) divided by the current, in amperes (I) – Ohm´s law.

As the length of the wire is increased the number of collisions the current carrying charged particles make with fixed particles also increases and therefore the value for the resistance of the wire becomes higher. Resistance, in ohms (R) is also equal to the resistivity of the wire, in ohm-meters (ñ) multiplied by the length, in meters (l) divided by the cross sectional area, in square meters (A).

The material and cross sectional area of the wire is constant throughout the experiment. Therefore it is clear from the formula that the resistance should be directly proportional to the length. Key factors: in this experiment we will only change one factor, the length of the wire. This should effect the resistance of the wire in the ways stated above. Fair test: in this experiment we are only changing one factor – the length of the wire, the factors that we are going to keep the same are as follows: We must keep the surrounding room temperature the same or the particles in the wire will move faster (if the temperature is increased) and this will therefore have an effect on the resistance. The cross sectional area of the wire must be kept constant throughout as well. This is shown in equation (2) where the cross sectional area is a factor that effects the resistance. The material of the wire must also be kept the same as different materials have different conductivity. The last two factors will be kept the same by using the same wire all of the way through the experiment. The current that we pass through the wire is to be kept the same, also. If this is changed the temperature of the wire might change in a way that is not constant making the results more confusing. Apparatus:

1. Wire, over 50 cm long

2. Rheostat

3. Power supply

4. Six connecting wires

5. Two crocodile clips

6. Voltmeter

7. Ammeter Plan:

1. Connect circuit as shown in the diagram.

2. Adjust rheostat until the ammeter reads .3 A.

3. Record voltage on voltmeter

4. Repeat the experiment with the following lengths of wire, connected between the two crocodile clips:

- 10 cm

- 15 cm

- 20 cm

- 25 cm

- 30 cm

- 35 cm

- 40 cm

- 45 cm

- 50 cm

5. Use Ohm´s law to find the resistance of the wire, equation (1). Diagram:

Safety: this is not a very dangerous experiment but despite this you must always handle electricity with care, keep the current low, handle with dry hands etc. Accuracy: to keep this experiment as accurate as possible we need to make sure, firstly, that the length of the wire is measured precisely from the inside edge of the crocodile clips, making sure that the wire is straight when we do this. We must also make sure that the wire is straight when we conduct the experiment. If it is not, short circuits may occur and bends and kinks in the wire may effect the resistance, also. The reading that we take of the voltage should be done fairly promptly after the circuit is connected. This is because as soon as a current is put through the wire it will get hotter and we want to test it when heat is effecting it the least, i.e. at the beginning. Preliminary: upon testing to see if the experiment would work I found no problems with the plan I described earlier. I was able to get the following results: LENGTH

(cm)CURRENT

(A)VOLTAGE

(V)RESISTANCE

(=V/I(Ù))

100.30.130.43

150.30.200.66

200.30.270.90

250.30.351.16

300.30.421.40

350.30.481.60

400.30.571.90

450.30.602.00

500.30.682.26

Observations Observations: we will observe the reading on the voltmeter change as we change the current to .3 A. we also observe a general increase in the voltage as the length of wire we use gets longer. The rheostat will also be set at different positions for the different lengths of wire that we use. Evidence: to make sure our overall values are as accurate as possible we will repeat our readings 3 times and then take the mean resistance of the 3 readings. We will also be able to spot and discard any anomalies from our results. Results:

Set (i)

Length

(cm)Current

(A)Voltage

(V)Resistance

(=V/I in Ù)

100.30.130.43

150.30.200.66

200.30.270.90

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