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# Investigate the effect of changing the length of a wire on the current flowing through it.

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Introduction

Aaron Atkinson 10/68                GCSE Physics: Coursework

GCSE PHYSICS COURSEWORK:

MODULE 5 ENERGY & ELECTRICITY

Investigate the effect of changing the length of a wire on the current flowing through it.

## Skill Area P: Planning

This coursework assignment deals with the relationship between the length of a wire and the current flowing through it. I will refer to other factors that determine current so that I can use scientific knowledge and understanding to turn ideas into an appropriate strategy. It is important to understand what current is to progress with the investigation.

-         Electricity is a flow of charged particles, which may be electrons or ions

• Current is the measure of the rate of flow of electrical charge. Electric current is measured in amperes, A. The ampere is defined in terms of the magnetic effect of an electric current.
• Electric charge is measured in coulombs, C. One coulomb is defined as the amount of charge passing a point in a circuit each second when the current is one ampere.
• Current will only flow through a component if there is a voltage across that component.
• The equation for current is defined as: I = V / R where I = current, V = voltage or potential difference or p.d., R = resistance.
• Voltage is the “push” or energy given to the charges (usually electrons).
• Ohm’s Law states that the current through a metallic conductor at constant temperature is proportional to the voltage.
• Resistance is measured in Ohms (symbol Ω). It is a measure of how much the current is slowed down. The bigger the resistance, the smaller the current.

There is of course a balance between voltage and resistance. The aim of voltage is to push the current around the circuit, and the resistance is opposing it – the relative sizes of the voltage and resistance decide how big the current will be:

INCREASE in VOLTAGE  INCREASE in CURRENT

INCREASE in RESISTANCE  DECREASE in CURRENT

If the resistance of a component is constant (stays the same) for different values of V and I, then a plot (graph) of V against I will be a straight line. The gradient (slope) of the line shows how big the resistance is.  There are also other factors that affect current:

• Material
• Temperature
• Thickness

Material – Certain types of materials have a greater resistance than others.

Temperature – an increase in temperature results from an increase in voltage, and essentially an increase in current. From this we can deduce that at high temperatures the resistance is lower.

Thickness – A wire with a greater thickness has a larger diameter for the electrons to flow through. This means there is more space for them to flow freely. The result  Resistance decreases.

In general:

Increase in voltage  increase in push on electrons  electrons flow faster  charge flows faster  Current increases/Resistance decreases

My hypothesis states that: “If I increase the length of a wire the effect on the current flowing through it will be that it decreases. If I decrease the length of the wire the current should increase”.

The effect of length on current is the key factor that I intent to investigate.

My statement can be backed up by the theory which states that:-

1. Electrons flowing through a material of a greater length have to travel a longer distance and so there is a greater chance for resistance to occur. Since there is more resistance, the current decreases.
2. Electrons flowing through a material with a small length have less distance to travel, there is less chance for resistance to occur and so the current increases. This can be reinforced by the fact that a shorter wire gets hot when electrons flow through it and this increase in temperature is a result of an increase in current as the electrons have more energy.

In order to carry out this investigation the following apparatus will be used:-

• Power pack
• Voltmeter
• Ammeter
• Variable Resistor (to maintain the voltage)
• Wire attached to a ruler of approx. 1m length (chosen type)
• Standard wiring for circuit
• Crocodile clips (to be clipped to chosen wire; the length of the wire will be altered depending on the position of the crocodile clips)

Middle   The voltmeter must be placed in parallel around the component (in this case the wire attached to the ruler). The component, ammeter and the variable resistor  are all in series and can be placed anywhere in the circuit.

This is a good way of carrying out the task. The circuit is simple and it’s structure enables us to take results effectively. The component coloured in red indicates that the length can be changed by moving the position of the crocodile clips on either end.

The procedure for taking results is as follows:-

1. Set the power pack to the desired voltage, for arguments  sake say 1V.
2. Check that the Voltmeter reading shows 1V, by using the variable resistor.
3. Now observe the reading on the Ammeter. The reading will probably change slightly continously but take a reading that is the most stable.
4. Record this reading on your table. The table should have a space for Length and Current.
5. Now shorten the length of the wire slightly by changing the position of the crocodile clips, maintain the voltage using the variable resistor, and jot down your reading from the ammeter.

This procedure should be repeated until you reach the minimum length. (The minimum length will be discussed in the preliminary section later on).

To ensure that obtain a good quality of results this experiment needs to be fair.

Conclusion

Range I

1V

16cm

0.84

90cm

0.16

74

0.68

2V

32cm

0.98

90cm

0.32

58

0.66

3V

58cm

0.92

90cm

0.49

40

0.43

3) Nichrome 0.31mm

Voltage

Min L

Current

Max L

Current

Range L

Range I

1V

15cm

0.45

90cm

0.07

75

0.38

2V

30cm

0.47

90cm

0.15

60

0.32

3V

40cm

0.49

90cm

0.23

50

0.26

The row highlighted in yellow provides us with the best conditions as it had the greatest overall range. We can deduce that Constantan 0.31mm was the best suite dmaterial for this investigation. The greatest range occurred when the investigation took place at 1 volt. The chosen maximum length was 90cm since there was tape stuck at the end of the stick. The minimum length before the wire was hot was 16cm but this can obviously vary. I decided to take readings for 10 values and to count down in intervals of 7cm from 90cm. This made the minimum value 29cm. In my opinion it is sufficient enough to take 10 readings as these can be analysed to observe a pattern or trend and to complete a smooth curve on a graph to demonstrate this.

Safety

Safety is of course important to take into consideration during all practical work in the laboratory. Overall the experiment is quite safe as I am not dealing with dangerous chemicals or radioactive substances. However, electricity is being used and it is important that care is taken at all times to avoid potential scenarios that may lead to electrical shock. This can be managed by:

• Ensuring there is no water near the work area.
• Being aware of the potential dangers of electricity.
• Managing the working environment to ensure the safety of myself and others.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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