Resistance occurs in circuits because of components in the circuit and a larger amount of resistance causes the battery to have to exert more energy to push the charges through the circuit. This then causes the current to decrease as resistance is not allowing as much current to flow. Resistance can be useful in some circuits. Devices called resistors are used to control the flow of charged in a circuit. Variable resistors can be used to make varying the size of the current easier as the size of their resistance can be steadily changed using a dial or slider.
Variable resistors are used in dimmer switches and volume controls like that of a CD player. Another type of resistor is an LDR, (Light dependent resistor) which is a variable resistor. This resistor’s resistance increases, as light levels decrease as it gets darker and decreases, as light levels increase during daytime. This makes LDR useful for example in automatic security lights. One finally type of resistor is a thermistor, which has a higher resistance at low temperatures and a lower resistance at high temperatures. A thermistor can be used as a temperatures sensor in devices like fire alarms.
There are five factors which could potentially affect the resistance of the wire in a circuit. These factors are: Changing the voltage of the battery, changing the diameter of the wire, changing the temperature of the wire, changing the material of the wire and finally changing the length of the wire. Changing the voltage, however will not affect the resistance of the wire. This is because preliminary work I carried out in class showed us that current and voltage are proportional to each other, if one of these increases by a certain amount, the other will also increase by this amount too.
This is ohm’s law, meaning that changing the voltage would also change the current by the same amount the voltage was changed by, therefore keeping resistance the same. This is shown by the formula I= V/R, where (I) is the current, (V) is the voltage and (R) is the resistance. Another factor that we can test is changing the diameter of the wire. A thinner wire would provide more resistance because there is less space for the electrons to pass, which would then cause the battery to work harder to push the wire around the circuit as there is more resistance.
On the other hand, a wire with a larger diameter would mean less resistance as there would be more space for electrons to pass through, resulting in the power source not having to work as much to push the electrons around the circuit. This factor would be possible to test in our class investigation because we have different diameters of wire already provided for us. To test this factor, we would need the wire board which has different diameters already attached to the board. We would also need wires for the circuit and crocodile clips to attach the wires to the different diameters of the wire we are testing.
We will also need an ammeter to measure the current and a voltmeter which will be attached to the circuit in parallel over the wire so the voltage passing through the wire can be measured. Equipment: * 5 thicknesses of Nicrome wire (Constantan wire cannot be used because we only have 4 thicknesses available) – 0. 16, 0. 25, 0. 31, 0. 40 and 0. 45 mm * A wire board * Voltmeter * Ammeter * Crocodile clips The independent variables for this factor will be the different diameters of the wire. The dependent variable will be the resistance. However one problem with testing this factor is the wire heating up.
This is because changing the temperature of a wire is one of the factors that can affect resistance and the wire heating up may affect the results we gain during the experiment. As well as this, we cannot guarantee that the thickness of the wire will be the same all through the whole wire. Changing the temperature of the wire could also affect the resistance of the wire. The higher the temperature of the wire, the higher the resistance will be. This is because a higher temperature would cause the molecules in the wire to vibrate more and they would be more likely to collide, which increases resistance.
The equipment we would need to test this would be the basic wire board, wires for the circuit, ammeter and voltmeter. We would need a thermometer or any other temperature recording device which would allow us to measure the different temperatures. We would also need something which would allow us to regulate the temperature of the wire so that we can increase or decrease the temperature of the wire. The independent variable would be the temperature of the wire and the dependent variables would be the voltage, current and resistance for each different temperature.
We would then have to keep the wire the same length, diameter and of the same material throughout the investigation. Equipment: A chosen thickness and length of Constantan wire Thermometer or other temperature sensor However we cannot test this factor in our investigation since we do not have the equipment to keep the temperature the same and it would also be hard to keep the temperature at a constant level as the wire would heat up anyway because of the current passing through it. Changing the material of the wire is another factor that could affect the resistance of the wire.
This is because the denser the material the wire is made from, the higher the resistance would be since the material would block more electrons, making it harder for them to go round the circuit and therefore increasing resistance. This factor could be tested by once again using the wire board, though this time attaching each of the different wire materials to it. There would also need to be the voltmeter and ammeter for measuring voltage and current. The variables we will have to keep the same are the length and diameter of the wires because these factors can affect resistance and therefore affect our results.
The temperature of the wire would also have to be controlled, so the current cannot go above 1A. Finally, we would also have to make sure that the purity of the wires was the same, meaning that the amount of the material in each of the different wires would have to be kept the same so that the test can be fair. However, this cannot be tested in our investigation because some materials would be too expensive to be purchased. Equipment: At least five different material types of wire Voltmeter Ammeter Another factor which can be changed to affect the resistance is the length of the wire.
The longer the wire is, the more the electrons in the wire collide with the fixed atoms in the wire, which increases the resistance because the fixed atoms block the electrons, making it harder for them to travel round in the circuit. We can test this factor because we can manipulate the length of the wire using crocodile clips. However one problem with testing this factor is that we cannot guarantee that the wire will be the same thickness all the way through the wire and one factor that we must keep the same is the diameter of the wire.
A way that we could check that the wire has the same diameter all the way through it is by using a micrometer and using it to measure five points on the wire. I have decided that the factor I will be investigation will be how the length of a wire affects the resistance. Preliminary During my preliminary work, I had to decide on an operating voltage so I tested different voltages on different wire thicknesses. Firstly, I tested two voltages on the thinnest wire, which was 0. 16 mm. I couldn’t record the data for 6 volts because the current would have gone to high and possibly damaged the wire. Key: Outlier
Power pack set to 4V Power pack set to 2V Length (cm) Voltage Current Resistance (? ) Voltage Current Resistance (? ) We then tested the two voltages on the thickest wire, which was 0. 40 mm. I found that the voltages of 2V and 4V both caused the current of the wire to go above 1 Amp. The current cannot be allowed to go above 1A because if it went above it, it would cause the wire to heat up and eventually start glowing or burning, which would damage the wire.
As well as this, there was one outlier in the data, which may have been caused by the ammeter being read wrongly since the current value in the first table for 40cm with the power pack set to 2V, was much lower than the other values. So I had to test the two other thicknesses of wire, 0.25 mm and 0. 31 mm with the results in the table below.
Thickness of wire: 0. 25mm (Power pack set to 2V) Length Voltage Current Resistance (? ) In conclusion I have decided that, the operating voltage I will be working with during my experiment will be at 2 volts.
This is because in my preliminary work, I have found that this voltage does not cause the current to increase above 1A. This is important since an increase above 1A because the temperature of the wire increasing may cause it to melt or break. As well as this, temperature is one variable we must try to keep the same so that our results are not affected by it. I cannot choose 1 volt as the operating voltage because when we tested different lengths of wire with that voltage, we found that the results didn’t vary by a noticeable amount and this would consequently make it hard to draw a conclusion for the investigation using that data.
The lengths I have chosen for my investigation are 20-100cm with intervals of ten centimetres. These lengths were chosen because when tested with my operating voltage of 2V, they were the lengths which did not make the current go above 1A, though the current result for 10cm was 1. 53 which went above 1A. The diameter of wire I will be using is 0. 25 mm because when we experimented with different thicknesses of wire, we found that 0. 25mm gave us results which did not go above 1A. The equipment I will need for the investigation is as follows: A wire board with Constantan wire attached A Voltmete* Ammeter Crocodile clips.
Power pack Wires for the circuit The independent variable I will be changing is the length of the wire. The dependent variable is the resistance of the wire and the variable we would need to control would be the temperature because temperature would affect the results of my investigation. The wires will be used for the circuit and the crocodile clips will be used to attach the circuit wires to the Constantan wire and also to change the length of the wire by using the wire board ruler to move the crocodile clips up and down the wire. The ammeter will be used to measure the current and the voltmeter to measure the voltage.
A multimeter can be used to measure the resistance, however we found through our preliminary work that the multimeter only calculates resistance to one decimal place and so isn’t as accurate as it can be. That is why I will calculate the resistance by using the results obtained for the current and voltage and Ohm’s law by dividing the voltage by the current to work out the resistance. This is much more accurate than using a multimeter because the ammeter and the voltmeter work out current and voltage to two decimal places, meaning that our resistance will be more accurate as it to will be worked out to two decimal places.
To make sure that the controls I will put on the investigation to make sure the test is as precise as it can be and the results are reliable and accurate, I will make sure that the material of the wire used each time is kept the same by using the same wire board for the whole main investigation so the material doesn’t affect the results I get. I will also make sure to keep the current of the circuit below 1A and the diameter of the wire the same for each test. Finally, to make sure the results I get are reliable, I will make sure to test the voltage and current for each length of wire at least three times.