Resistance ( R )= p.d. across the wire ( V )
Current through the wire ( I )
V = voltage or potential difference in volts (V)
I = electric current in amperes or amps (A)
R = resistance to the current in ohms (W)
You can remember it easier in a triangle formula: -
Before starting the experiment I have decided to choose one factor that will affect the resistance of a wire. I shall do this by going through all of the factors that affect the resistance of a wire and how I would measuring each factor to find out which would be the most effective and easiest factor to measure.
There are four factors that effect resistance.
Wire length: If the length of the wire is increased then the resistance will increase as the electrons will have a longer distance to travel through the wire and so more collisions will occur. This length increase will be proportional to the resistance increase.
Thickness: (cross-section area) If the wires width is increased the resistance will decrease. This is because of the increase of space allows the electrons to travel through easily and not collide. This increase in space between
the atoms means there should be fewer collisions.
Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of the increase in energy. This causes more collisions between the electrons and the atoms. This increase in collisions means that there will be an increase in resistance.
Material: The type of material will affect the amount of electrons that are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if the atoms are larger atoms will have more electrons. If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons. If the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.
From this list of factors I shall only pick one factor to investigate, the factor I will investigate the length of the wire.
In this experiment I will use:-
A power pack,
Leads,
Bare constantan resistance wire (0.704),
A ruler,
Voltmeter,
an ammeter and,
2 crocodile clips to clip to either end of the wire.
You set up the circuit like this
Prediction
I predict that as the length of the wire increases the resistance will increase. This happens because the electrons will have a longer distance to travel through the wire and so more collisions will occur increasing the resistance.
Method
1. Set up the circuit.
2. Vary the dial on the power pack to get 0.3, 0.6, 1.0, and 1.5 on the ammeter and calculate the resistance.
3. Repeat this at 10,20,30,40,50,60,70,80cms.
4. Each time take the reading from the voltmeter and put on a table of results.
5. Plot graphs for each set of results and a graph of the averages.
Results
10cm
20cm
30cm
40cm
50cm
60cm
70cm
80cm
