Investigating One Factor Which Affects the Resistance of a Wire

Material it is made up of - some materials have less resistance than others. They have fewer atoms therefore there are less atoms for the electrons to collide with resulting in a lower loss of energy.

Temperature it is at - the higher the temperature, the lower the resistance and visa versa.

I have chosen to look at how the length of the wire affects the resistance because it is the most simple to obtain results from in a school lab.

Plan

To conduct this experiment accurately I will need the following equipment:

* Power supply - to provide electricity

* Wire - to test for resistance

* Ammeter - to measure current in the circuit

* Digital voltmeter to measure voltage in the circuit

* Switch - so the circuit can be switched off when not in use

* Leads - to run electricity to all the components

* Crocodile clips - to hold the wire in place

* Metre ruler - to measure the length of the wire

* Wire cutter - to cut the wire up into smaller pieces

Method

This is a diagram of the circuit I will be using.

I will set up the circuit, as above, for this experiment. The voltmeter will record the voltage used up through the wire. The ammeter will record the current. These two recordings can then be used to work out the resistance in the wire.

I will need to draw a graph with my results. In order for the graph to show a clear picture of what is happening the results will need to be accurate. To collect accurate data I will do the following:

* record readings to two significant figures

* measure length of wire accurately

* make sure there is minimum kinks in the wire which would affect the length

* make sure the current is the same throughout the experiment

The length of wire will have a range from 0.1 meters to 1 meter. I will have to keep the current constant at about 0.6 amps.

Safety

To insure that I or anyone else, don't get hurt, I will take the following precautions:

* I won't touch the wire in case it's hot and I get burnt or in case I get a shock

* I'll turn the switch off when I'm writing down results so it doesn't heat up

* I'll wear safety goggles in case the wire snaps and hits me in the eye

* I'll bend the wire at the edges so there are no sharp ages I could cut myself on

* I will sellotape the wire down so it doesn't bounce up and hit someone

* I'll keep flammable materials away from the circuit

Recording the Data

This is the table I will use to record the data.

Wire

Length (m)

Voltage (V)

Current (A)

Resistance (?)

Test 1

Test 2

Average

0.6

0.9

0.6

0.8

0.6

0.7

0.6

0.6

0.6

0.5

0.6

0.4

0.6

0.3

0.6

0.2

0.6

0.1

0.6

This is an outline of the graph I will draw.

To find the resistance (R) I will have to use the following equation.

resistance = R =

1.8

e.g. R = 1.2 R = 1.5 ?

The potential difference (P.D.) is the voltage (V) used up in the wire.

Resistance is measured in Ohms (?).

I predict that as the length of wire increases, the resistance will increase proportional to the length of the wire. E.g. length 0.5m resistance 1.2 ?

length 1m resistance 2.4 ?

As the length doubles so will the resistance. This comes from Ohm's law, which is quoted on the first page.

This is what I

predict the graph

will look like. A

straight line and

a positive

correlation.

Resistance

proportional to

the length.

What the Results Tell Us

From the data I have collected I have proved that Ohms Law and my predictions, were correct. As you can see from the graph the resistance increases as the length of wire increases. Like I predicted, the graph forms a positive correlation and an almost straight line. This tells is that the resistance of the wire is directly proportional to the length of the wire.

The results aren't in a completely straight line because:

- there were a few kinks in the wire I couldn't get rid of;

- the wire might have warmed up slightly towards the end of the experiment due to the electricity running through it and

- the ammeter and/or voltmeter might not have given accurate readings.

Even though the results aren't completely accurate, they are still good enough to draw up a conclusion.

To collect more accurate data I could have done the following:

- use a stronger tape to hold the wire down when measuring so there would be no kinks;

- leave some time after each reading to let the wire cool down;

- use a digital ammeter and

- use a more accurate voltmeter.

Why the Length Affected the Resistance

The length of the wire affected the resistance because the longer the wire, the more atoms the electrons collided with resulting in the loss of more energy.

short wire long wire

electron atom

As you can see the from the diagrams, there are more atoms for the electrons to collide into in the longer wire than there are in the short one, hence more energy being lost. There is little resistance in the leads running electricity to the wire because they are made out of copper. Copper is a very good conductor and electrons can flow through it without colliding with many atoms.

Conclusion

I have found out in this experiment that:

- as the length of a wire increases so does the resistance.

- Ohms Law, which states that the resistance of the wire is proportional to the length, is correct due to the fact that as the length of my wire increased so did the resistance e.g. wire length 0.3m, resistance 0.6 ?

wire length 0.6m, resistance 1.21 ?

These points also prove my predictions were correct.