To find out how the length of a piece of wire effects the reaction time in a circuit.

To keep the experiment a fair test I will use the same wire each time. If the experiment takes longer than one lesson I will have to store the wire in a safe place where it won't get lost or tangled up. I will also use the same ammeter and voltmeter each time. This is because some of the school ammeters and voltmeters are not completely accurate in their readings. I will also make sure the wire is straight and not touching at any point. This is because if the wire is touching then the current will flow through the smallest route missing out a large chunk of the wire and changing the length of wire used. The crocodile clips will also have to be connected at the very end so that I don't loose any millimetres behind the clips.

Step by step method:

· I will get my equipment

· I will set up the circuit

· I will cut the wire and make sure it is exactly 50cm long

· I will attach the wire into the circuit, making sure the crocodile clips are positioned at the very end of each end of the wire

· I will put the resistor at no resistance and switch the power on

· I will record the results. With the results from the ammeter and voltmeter.

* I will then repeat the experiment with the same length wire and the resistor at 1/4 way across

· I will record the results

· I will then repeat the experiment with the variable resistor at 1/2 way across

· I will then have 3 sets of results in the ammeter and voltmeter columns for 50 cms of wire. From these results I can get an average. Then using the average I can work out the resistance.

To get the resistance I divide the current by the voltage. The formula for this is:

· I will then repeat the experiment and the above bullet points for the other lengths of wire.

· The wire looses 5cm each time.

Equipment needed:

x Wire at 50cm

Wire cutters

Variable power supply

Variable resistor

Ammeter - for measuring current

Voltmeter - for measuring voltage

The circuit:

= Voltmeter

2 = Variable resistor

3 = Ammeter

4 = Wire, 50-5cm long

5 = Variable power supply set at o.6v

Prediction:

I think that the shorter the wire is the less resistance there will be. This is because the longer the wire the further the electrons have to travel to carry on around the circuit. So because the wire is shorter the electrons don't have to pass as many ions. So the longer the wire is the more ions the electrons have to pass therefore the more ions the slower the electrons will be. Then this will be causing more resistance.

Results:

Length of wire (cm)

Voltage (v)

Current (amps)

Resistance (ohms)

Average resistance (ohms)

Try 1

0.2

0.15

.3

50 cm Try 2

0.3

0.3

.0

.1

Try 3

.0

.0

.0

Try 1

0.2

0.2

.0

45 cm Try 2

0.3

0.3

.0

.0

Try 3

0.8

0.85

0.9

Try 1

.6

0.8

2.0

40 cm Try 2

0.9

0.45

2.0

2.1

Try 3

0.7

0.3

2.3

Try 1

.4

0.6

.8

35 cm Try 2

0.85

0.5

.7

.7

Try 3

0.6

0.35

.7

Try 1

.4

0.95

.5

30 cm Try 2

0.9

0.6

.5

.6

Try 3

0.6

0.35

2.0

Try 1

.4

.25

.1

25 cm Try 2

0.9

0.7

.3

.2

Try 3

0.4

0.35

.2

Try 1

.2

.35

0.8

20 cm Try 2

0.6

0.5

.2

.1

Try 3

0.4

0.34

.5

Try 1

0.1

.4

0.1

5 cm Try 2

0.45

0.6

0.7

0.5

Try 3

0.3

0.45

0.6

Try 1

.0

.6

0.6

0 cm Try 2

0.3

0.5

0.7

0.5

Try 3

0.25

0.35

0.3

Try 1

0.6

2.0

0.3

05 cm Try 2

0.2

.7

0.2

0.2

Try 3

0.1

0.45

0.2

Conclusion:

From the results gathered I can conclude that the shorter the wire the lower the resistance. I can tell this as the resistance decreases as the length of the wire gets shorter. At the beginning of the experiment I made my prediction. This was that, as the wire got shorter the resistance would go down. I thought resistance would go down because the electrons would have to pass through fewer ions to carry on around the circuit. Therefore everytime I decreased the length of the wire by 5 centimetres I would be cutting out millions of tiny ions that make up that 5cm of wire. So as the electrons don't have to pass as many ions which slow them down and cause a build up (resistance) the electrons should be able to pass around the circuit in a faster time. If the electrons are passing around the circuit faster this means that they are not being held up as much.

So in conclusion, I made my prediction at the beginning and it was correct. The shorter the wire the less resistance. This is proven in my results.

Evaluation:

I think that the experiment went to plan quite well. Most of my results were correct except 2 lengths. I followed my plan of action and my step by step method very closely in an attempt not to make any mistakes.

I managed to use the same ammeter and voltmeter each time so my results should not have varied much between the two lessons they were recorded in.

The only problem that I encountered is that the wire from the first lesson got snapped causing us to have to get a new wire. The new piece of wire was actually of different thickness to the first wire. You can see this when you look at the result table. The 50cm and 45cm points are completely separate from the other results.

If I was to try the experiment again I would try and be more accurate in my reading if the voltmeter and ammeter as I probably miss-read the results slightly each time. I would also get a voltmeter and ammeter that was more accurate.

I would also make sure that I used the same wire each time as this messed up my results for the 50 and 45cm length of wire.