How temperature affects resistance on a piece of wire: Resistance is how ‘hard’ it is to ‘push’ a current through a substance. There are 4 main factors which effect resistance: – (i) Length to travel – the further the electrons has to travel the higher the resistance (ii) Temperature – the higher the temperature the more energy the electron has, the lower the temperature the lower the energy of the electron, with more heat the resistance drop and vice versa (iii).
Cross-sectional area – the larger the cross section the lower the resistance (iv) Type of metal – different metals have different resistances How do I find out the resistance of a component in a circuit: Get an amp meter and put it in series, get a Volt meter and put this in series with the component, to find the resistance you use the equation: ‘I’ being the current ‘R’ being the resistance ‘V’ being the voltage or potential difference You need to rearrange the equation so that resistance = voltage over current:
All you need to do is input the voltage (in Volts) over the current (in Amps) and your result is resistance. In my investigation, I have chosen to investigate the effect of temperature on resistance in enameled copper wire, I have chosen to do this because: – (i) I have certain hypothesis of how temperature affects resistance (ii) I have chosen enameled copper wire as I will be using long lengths I do not want to short circuit the wire when they are wrapped hence the enamel.
I chose copper because it is meant to be used as an electrical conductor (e. g.wire) compared to nichrome wire which is for use for heating elements (this would affect temperature and make my investigation un reliable) and constantan which is used for making resistors (heat doesn’t change its resistance much) (iii) ln my preliminary work I found that a short piece of copper wire isn’t enough to show a change in resistance, so I immediately scrapped the idea of using a length under 2m.
I found that with different lengths yielded very different results – Using 10 amp range on meter – With 50cm I got: Cold Water: Amps =0. 1007 Voltage = 0. 03 Resistance = 0.297 ? Hot water: Amps = 0. 1002 Voltage = 0. 04 Resistance = 0. 399 ? With 5m I got: Cold Water: Amps = 0. 57 amps Voltage = 1. 43V Resistance = 2. 49 ? Hot Water: Amps = 0. 47 amps Voltage = 1. 45 V Resistance = 3. 085 ? With 10m I got these results: Cold Water: Amps = 0. 0748 Voltage = 0. 41.
Resistance = 5. 481 ? Hot Water: Amps = 0. 071 Voltage = 0. 46 Resistance = 6. 478 ? These results show me that using a longer wire is going to produce more precise results, I get more precise readings on the volt meter and amp meter which is going to produce more accurate resistance readings.
To keep the result as reliable as possible I will do the experiment at least 3 times (ideally more if times permits) each time changing the wires/ equipment (apart from my testing wire) and take the measurements again. I am going to use a 10m length of enameled copper wire Equipment I will need to use: Amp meter – I will need to measure the amps to find out the resistance Volt meter – I will need to measure the volts to find out the resistance . Variable Resistor – to keep the current of the circuit under 200mA so I can use the 200mA range on the Amp meter – this is because I can gain more precise results.
Batteries or power source – Obviously I will need to power the circuit, a power supply would be better as I always get the same voltage/current, these are not available so I will have to use batteries, the power they supply shouldn’t make too much difference to the results Wires – to connect the circuit up Crocodile clips – to attach the wires to my ‘testing wire’ Enameled copper wire – this is what I am testing the resistance of. I will use temperatures from 0 i?? C – 100 i?? C if it is possible to achieve such extremes with a kettle and ice.