Measuring Resistance

Measuring resistance coursework

Aim: To investigate how the resistance of a wire is affected by its length

Introduction

In this investigation I will carry out an experiment to distinguish how the length of a wire, disrupts the behavior of the resistance.

Resistance is anything that causes an opposition to the flow of electricity in a circuit. It is used to control the amount of voltage and/or amperage in a circuit. Everything in a circuit causes a resistance. Resistance is measured in ohms. Resistance occurs when the electrons traveling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire. The resistance of a wire depends on the number of collisions the electrons have with the atoms, if a larger number of collisions occur, the resistance of the wire will increase. To calculate the resistance of a wire, I will use ohms law, which is: V=IR, therefore R=V/I.

The resistance of a wire can be affected and altered by the current, the length of the wire, the thickness of the wire, and the temperature and material.

Particles in metals are tightly packed together because it is a solid. Metals contain free electrons which allow electricity and heat to be able to pass through and this is why they are good conductors. The structure of metals give them special properties, these properties are:

* The atoms are packed closely together in a regular pattern to form a big structure; this causes many metals to be dense.

* The electrons in the outer energy levels of the metal atoms are able to move around the structure, therefore metals conduct electricity.

* The forces holding the atoms are strong. Most metals don't dissolve in solvents and have high melting and boiling points.

To make sure that I get very accurate results, I will repeat all my measurements, and I will be aware of the risk assessment with this experiment. I will not touch the wire when the current is flowing so I do not receive an electrical shock; I will keep the current low so if I do touch the wire it will not be too dangerous. I will keep the temperature constant to make it a fair test. The ends of the wire are sharp so I will make sure that I don't cut anyone with them. I will also switch off all equipment when it is not in use to reduce the probability of an accident occurring and also to minimize the use of electricity.

Preliminary experiment

Before I begin the main experiment, I must do a preliminary experiment. In this preliminary experiment I will measure the voltage and amperage of two different types of wire and use different thicknesses of these wires to see which type of wire and thickness will be the best to use in my main experiment. I will use the wire that will give me largest resistance, because this wire will be the best to use in the experiment because it will give me the most accurate results. In this experiment I will keep the length of the wire the same so it is a fair test.

The variables in this preliminary experiment are:

* length

* width

* temperature

* type of metal/material

Apparatus

The apparatus that I will use in this experiment are:

* Ammeter

* Voltmeter

* Power supply

* 4 connecting leads

* 2 crocodile clips

* meter ruler

* tape

* constantan and nickel chrome wire

* variable resistor

* wire cutter

Method

1) cut a length of wire 50cm long

2) Use tape to fasten the wire to a meter ruler. Try to keep the wire straight and avoid kinks.

3) Using crocodile clips to connect onto the wire, make up the circuit shown below in the diagram.

4) Check that the ammeter registers a reading and then add the voltmeter in parallel with the wire.

5) Repeat the experiment, using the different types of wire and different lengths.

Diagram

Results

METAL THICKNSS VOLTMETER AMMETER RESISTANCE

constantan 34 0.6 0.1 6

constantan 18 0.1 0.1 1

constantan 36 1.2 0.08 15

Nickel chrome 22 0.2 0.1 2

Nickel chrome 26 0.5 0.1 5

From my results for my preliminary experiment I can see that the highest resistance in the table is 15. The metal for the highest resistance is constantan and the thickness of the metal is 36. This is the metal and thickness that I will use in my main experiment. I think that from observing my bar chart that the higher the thickness is, the larger resistance it has.

Main experiment

Now that I have decided that I will use the metal constantan and will make it 36 in thickness I will now go on to my main experiment. In this experiment I will vary the length of the wire in my circuit