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Resistance of a wire - a number of experiments were carried out to determine different variables affected resistance.

Extracts from this document...

Introduction

Science Investigation

Resistance of a wire coursework

P

O

A

E

Total mark =

30

Preliminary Work:

        As part of the first module to be studied at GCSE (module 5), a number of experiments were carried out to determine different variables affected resistance.

image08.png

Experiment 1 – Proving Ohm’s Law

The circuit opposite can be used to investigate the relationship between the current flowing through the fixed resistor and the potential difference (voltage) across the fixed resistor.

The variable resistor is used to change the current flowing around the circuit. If the position of the variable resistor is changed in regular increments, the ammeter and voltmeter readings can be recorded and the results plotted on a graph.

Ohm’s Law states… The current through a metallic conductor is directly proportional to the potential difference across its ends, providing the temperature and other conditions are constant.image00.png

V=IR

Experiment 2 – Investigation the equation

R=ρL/A

L = Length, ρ = resistivity, A = Cross – sectional area

        For the second set of experiments, a number of lengths of wire were crammed between two pieces of A4 white card and fixed in place using staples. These lengths of wire were used as fixed resistors.

        The same apparatus was used for Experiment 2 as in Experiment 1 above, but the fixed resistor was replaced by each of the wires, in turn, stapled onto the card. Crocodile clips were attached to the staples at each end of the wire and the ammeter and the voltmeter readings were recorded.

        To make the experiment a fair test each wire had the same cross sectional are and was the same length between the staples. The following wires will be used:

  1. Single length of nichrome wire
  2. Single length of copper wire
  3. Single length of steel wire
  4. Single length of constantan wire
  5. Double length of constantan wire
  6. Triple length of constantan wire
  7. Single length of constantan wire (10cm,  20cm, 30cm)

The conclusion drawn

  • Types of wire        - Comparing wires made from different materials. It was found that    each different type of wire had a different resistance. Therefore, it is fair to conclude that the resistance of a wire depends upon the resistivity of the wire, i.e. its ability to resist the flow of charge.
  • Thickness of wire        - Comparing wires which had different thicknesses. It was found out that as the thickness of the wire increased the resistance decreased. Therefore, it is fair to conclude that the resistance o f a wire depends upon the thickness of the wire, i.e. its cross section area.
  • Length of wire        - The crocodile clips were attached at three different points along the wire, in turn in order that the resistance could be calculated. It was found out that as the length of wire increased the resistance increased. Therefore, it is fair to conclude that the resistance of a wire depends upon the length of the wire.  

The investigation to be undertaken

Of these three factors tested in experiment 2, the length of wire is the easiest variable to be investigated. Length is continuous variable and it is very simple to gather a large range of measurements.

The cross sectional area and resistivity of the constantan wire used in experiment 2 will be used in the investigation because it gave some good results in the range of apparatus.

Consequently, the investigation to be undertaken will be into how the length of a conductor affects the resistance of the conductor.

Aim:

The aim of this investigation is to determine how the length of a wire affects resistance.

Theory

Introduction

The Theory is split up into four different parts. They are:

  • The Metallic Structure of a Conductor
  • How a Metal Conducts Electricity
  • The Obstacle Model of Resistance
  • The Factors affecting Resistance
...read more.

Middle

When you move the slider to position 2, the light will go dimmer because it has to go through more coiled wire, whereas if you move the slider to position 3, the light will go brighter because it has less coiled wire to go through.

This variable resistor has 3 connect points, but you don’t use one of them. You can move the slider to brighten the light bulb.

What is current?

Current is a group of electrons that move very fast in different directions. They move very fast around a circuit.

Equation for current is: I = Q/t

                          Current = Change/time

The shorter the time the higher the current will be.

What is Voltage?

image11.png

When the battery is put into the circuit, chemical energy occurs in the cells and the cells are often referred. The cell pumps electrons around the circuit. This reaches the bulb, which then produces light and heat energy.

Voltage (potential difference, p.d) is a measure of how much electrical energy can be transferred per unit of charge. When thinking about charge a larger number of electrons are considered. This larger number of charge is called the coulomb. The reason is the charge of the electron is extremely small.

V = w/Q

V = voltage, w = work (joules, change in energy), Q = charge    

Voltage or potential difference is a measure of the difference of electrical potential energy of electrons between two points.

        W = V*Q

        C = 6*1018

        Each electron has 5J and when they go down the circuit after being pushed out of the cell. When they reach the beginning of the first voltmeter, they still have 3J left. However, when the electrons reach the middle of the two voltmeters they only have 1.5J left because the first lamp has used the other half of the energy.

...read more.

Conclusion

Was this a suitable procedure?

        It was a suitable investigation because I got what I expected and it proved my prediction. Also, a lot of people done this investigation like this because it is good. My graph is also good, so I know the suitability of the investigation is positive.

Was the evidence sufficient to support a firm conclusion?

        Yes, because if you look at my graph, it was done to a good degree of accuracy. As the length doubled, the resistance also doubled, so it was reliable. Also the % of error was less than 5.00% all the time. The replicates are close to the average. I got what I wanted because I did some research so I knew what to expect.

How could the investigation be improved?

Improvements

        I would do the experiment more time to get a better average. I would do the investigation 3 times which would mean I could do it on 3 separate graphs with the same apparatus. I would also use a longer wire from 1m to 2m.

Further work

        After doing this investigation, I could investigate another variable such as resistivity (type of wire).

        I would do the experiment by doing the following;

  1. I would set up the apparatus.
  2. I would cut 30cm of copper, tungsten, constantan, nichrome and steel wire.
  3. I would measure the voltmeter and ammeter readings.
  4. I would calculate the resistance.
  5. I would repeat the experiment 3 times to get an average voltage and an average current.

...read more.

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