Resistance is the force that opposes the flow of electrons in a circuit. The equation for resistance is Ω=V/A. (Ohms equals Voltage divided by amps). Resistivity is a measure of how strongly a material opposes the flow of electrical current, There are four main factors that affect resistance:
Length – this is because the electrons would bump into more atoms, the longer the wire which is like using up its fuel. Material – different materials inherent resistances as they have more or less atoms in them already. Thickness – Thickness affects resistance because the thicker the wire the more paths the electrons have to avoid the atoms. Therefore the cross sectional area is larger so there is less resistance. Temperature – The hotter the wire is the more energy the electrons have to flow faster. Why do we get resistance? An electric current flows when electrons move through a conductor. The electrons collide with atoms of the conductor causing resistance as this makes it harder for the current to flow. Electrons collide more often in a long wire than they do in a short wire. A thin wire carries fewer electrons so the resistance is lower. This means the resistance of a wire increases as: -The length of the wire increases
-The thickness of the wire decreases
The diagram below shows the collision between electrons and atoms in a wire.
Pilot Experiment 1/3: Nichrome
In order to test resistivity, we took measurements of the same metal by running an electric current through it. After completing the circuit, it was then possible to read the voltage and current from the voltmeter and ammeter. The idea of the experiment was to test the resistivity of a metal with varying lengths. For our first pilot experiment, we measured the resistivity of a Nichrome wire; I did this experiment to see whether the length of a wire affects resisitivity. Power Supply
+ 4V -
Amp & Volt Meter
Equipment List –
Crocodile Clip x2
* I attached all the components in a parallel circuit together as shown in the diagram above in order for the circuit to work properly. * Turn on the power supply on D.C (direct current) and onto 4 volts and no higher or the wire will over heat and burn. * Then attach your amp and voltmeters where required and view the readings and record them in your table. * Finally, record the results on your table and work out the I and R using ohms law. Results Table
Length/CM| Voltage/V| Current/Amps/I| Resistance=V/I|
7| 1.9| 4.0| 0.5|
9| 2.3| 3.4| 0.7|
11| 2.5| 3.0| 0.8|
I realised that the longer the wire the more resistance there was. I also established that the lower the voltage, the higher the current. As the length of the metal wire increased, the voltage increased and the current lowered. We also establish that the higher the voltage, the higher the resistance would be.
Pilot Experiment 2/3: Copper & Constantan
+ 2V -
In our second pilot experiment we tested the resistance of Copper, Constantan see in different materials of wire affect the resistance. The idea of the experiment was to test the resistance of the 3 different wires.
Amp & Volt Meter
Copper OR Constantan Wire
Equipment List –
Crocodile clip x2
* I first connected the Copper wire
* I used the longest length form our previous experiment which was 11CM * I connected the 2 crocodile clips to the wire
* I used 2 volts instead of 4 volts with a D.C current
* My circuit was connected in series rather then parallel * I then...