Resistance Investigation
Aim: to find out if resistance is affected by the length of Constantine wire in a circuit


Variables that need to be considered are the length, temperature, material and size of wire as these can vary the amount of resistance. I will choose one factor that will affect the resistance in a wire to find out if it is the most effective and easiest to measure.


The Independent variable I have chosen is length- the wire will be measured using a metre ruler. An ammeter and voltmeter will measure the amount of current and voltage across the wire depending on the amount of resistance given by a variable resistor. The length of wire will change after the five readings taken from each length set at 5cm intervals between 5 and 30cm.


The Dependant variables are resistance of wire, current and voltage, which means that these factors change according to each other.


Control variables


1) The material will be kept the same (Constantine wire).


The type of material will affect how many electrons will be able to flow through the wire. To see if the material was going to change how much resistance was to flow through I would record the difference in resistance of different types of wires by measuring the voltage across each one


2) The width will be kept the same as 0.31mm.


If the wire had a larger width then the resistance will decrease, as there is more space for the electrons to flow


3) The temperature will be controlled and kept constant by switching off the Power unit after every reading taken. To do this accurately one person would switch on the power unit and the other partner would take down the readings so it will stop the wire from heating up and altering the results. Temperature must be constant to obey Ohmís law which is V=IR, it means that if temperature increases then the atoms inside the wire will vibrate quicker therefore decreasing the speed of electron flow as it is more difficult for the electrons to pass through. This also means that resistance will increase so temperature must be kept constant in order for the experiment to be accurate and efficient. Another way of keeping the temperature constant is to draw a graph after taking the readings and cut off the results that show that the temperature has affected it.


This idea may not be as efficient as the first


4) The time must be kept the same to make the results unbiased so the circuit will be kept flowing for 2 seconds for each set of readings by using a stopwatch

Method
To investigate the amounts of resistance in a Constantine wire in a circuit I will set up an experiment as shown below. Using a power pack, a voltage will put be across the circuit and readings from the ammeter and voltmeter will be recorded at 5 cm intervals on the wire (from 5-30cm) held in place by crocodile clips on the metre ruler. (The wire needs a potential difference so the electrons can move in the wire with a force). The variable resistor will help to make the experiment more accurate because 5 readings will be taken at each point by varying the resistor so on a graph an average resistance can be calculated by finding the gradient making the experiment more precise.


The safety precautions needed to be considered- use sellotape in order to hold the wire down to the metre rule because as the wire gets hot masking tape wonít be efficient, as it will burn. Also make sure that the crocodile clips arenít in contact otherwise an electric current will be created which will affect the experiment. The power pack should be switched off straight after each set of readings so the wire has a chance to cool down and temperature will not affect the outcome of the experiment.


Prediction: I think that as the length of wire increases the resistance will also increase because there are more atoms in the longer wire for the electrons to collide with so it takes a lengthier time for the electrons to flow, therefore increasing resistance. Inside the wire there are also impurities like free electrons and atom nuclei, which also slow the