CourseworkHelp

Resistance Investigation

Planning
Aims and hypotheses
This investigation is designed to look into the resistance of different material in the form of wires and their conducting capability in different shapes. In order to do so, the materials are to be tested for their resistance in the shape of wires, and the hypotheses are such that different thickness and length of the wire and the material that makes up the wire itself will affect the electric conduction capability. Hence, the factors are:

* The thickness of the wires: 1, 2 , 3and 4 mm in diameter
* The length of the wires: 25, 50 , 75and 100 cm long
* The material of the wires: copper, iron, constantan and nichrome
* There will be 16 tests to be carried out

The experiment will require both the readings of voltage and current in order to produce the value of resistance according to the formula:

R = V/I ??
(Resistance is measured in Ohms)

The power supply, however, is varied between 0-12V with 1V interval so that a series of results can be obtained with the single factor altered: a graph of V against I can be drawn and an average resistance can be produced in this case, rendering it a fairer test. Since each test does not take long, the tests can also be repeated to obtain a more accurate mean. DC supply is used so that the voltage and current are not fluctuating while a steady reading is needed to be obtained.

To make it a fair test, only one factor should be altered at a time. When the material of the wire is being tested, the length and the diameter of the wires should be the same at 1mm wide and 25cm long. When the length and the diameter are being tested, the wire used should be made of copper, with the diameter and length remaining at 1mm and 25cm where possible.

Prediction
* An atom consists of a nucleus and orbiting electrons. These electrons can create a flow of current, so the more free electrons there are, the more conducting capability that material has; thus copper is more conductive that iron. Alloys tend to have less free electrons so they will be less conductive. The order of resistance is consequentially copper, iron, constantan then nichrome increasingly.
* Wires with wider diameter have more free electrons because the cross-section surface area is larger in proportion to the length, so the wider the wires are, the less reactive they would be. Resistance is proportional to the cross-section are of the wire given that the length and the material should be the same.
* Longer wires will cause an increase in resistance because the electrons have to travel past more atoms and collisions between the electrons and the atoms are more likely then in shorter wires. Resistance should also be proportional to the length of the wires.

Methods

The equipment needed consists of:

* A variable DC power pack
* Ordinary wires
* An ammeter
* A voltmeter
* 2 crocodile clips
* Assorted wires for tests

Then a circuit is set up in the same way as the illustrated diagram below.

* Connect the wire to the circuit by the crocodile clips
* Take the voltage and current readings from the meters
* Increase/decrease the supply from the power pack and take the readings again
* Repeat the experiment with different pieces of wire

Safety precautions

* Make sure that the circuit is properly connected before turning the power supply on, and do not touch the apparatus, especially the tested, naked wires until the power is switched off
* The changing of the tested wires should only occur when the power is off
* Do not carry out the experiment in wet areas, as water is a very good conductor.
* Do not switch on the power pack when there is no resistant wire and do not

If you still can't find any of the coursework that you are looking for, click here to look at over 30,000 GCSE, A-Level and University Level essays on Coursework.Info.