Typical setup To Measure The Resistivity Of A Wire
Note:that the Battery/Cell and rheostat (variable resistor) can be replaced by a variable Power supply
- 1m of constantan wire of nominal diameters 0.27 and 0.56 mm,
- 1m of nichrome wire of nominal diameters 0.27 and 0.56 mm
- Constant Voltage supply (constant meaning that changes will not be significant during the experiment),
- Either two multimeters or one ammeter and one voltmeter
Procedure When handling the wires avoid stretching them or deforming by kinking. this introduces local restrictions that will affect the results.
- Take one of the pieces of constantan wire and record its diameter in three places using the micrometer screw gauge. Calculate the average. Set up circuit as shown in the diagram. The Resistance R is the resistance wire (constantan nichrorome) that you will be trying to calculate.
- Set the power supply to 1V. This limits the current through the wire in order to reduce any heating effect which may change the resistivity.
- Record the readings on the ammeter and voltmeter for 8 different lengths.
- Complete a table a suitable table and calculate the resistance of the wire for each length.
For each wire plot a graph of resistance (y-axis) against length.
The resistance of a wire is given by the equation: R = ρ x l/A
Where R is resistance, ρ (pronounced 'rho') is the resistivity of the wire, l is length and A is its cross-sectional area.
The gradient of each graph will give you the quantity ρ /A
Therefore if you multiply the gradient by the cross-sectional area, this will give you the resistivity of the wire. (you can use the measured diameter to calculate the wire’s cross-sectional area)
Use the above method of analysis to calculate the resistivities for each wire.
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Investigating how the Resistance of a Constantan Wire is Affected by Its Length
- Length: 829 words (2.4 double-spaced pages)
- Rating: Excellent
Investigating how the Resistance of a Constantan Wire is Affected by Its Length
Introduction: In this experiment we will be investigating how changing
length of a piece of Constantan wire will affect the resistance.
Therefore the length will be an independent variable and all of
the other variables we will try to keep the same. The other
variables included in this experiment are temperature, thickness
of wire and density of wire. Resistance is a force, which
opposes the flow of an electric current around a circuit so that
energy is required to push the charged particles around the
- Thickness of the wire: if the wire is thin, the electrons are forced
to travel through a smaller area, therefore colliding more frequently,
resulting in them giving up more of their energy to surrounding
- Temperature: resistance of the wire increases as the
increases, as the atoms are oscillating faster. When an electro
collides with an atom, it loses its energy. If the wire cools, the
resistance will decrease.
- Length of Wire: the longer the wire the larger the resistance, due
to the fact the electrons have a further distance to travel,
increasing the possibility of any potential collisions.
- Wire density: If the wire has a high density, the resistance will
Higher, as there are more atoms found in a smaller space. This leaves
less, and smaller, gaps for the electrons to flow through. Because of
the lack of space, we would expect there to be more collisions between
the atoms and electrons.
- The reason for doing preliminary research was to get an indication
of the patterns I could expect in my results. Also, it was considered
a practice, so if any errors were made in the first attempt, then they
could be eradicated in my real experiment.
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Constantan Wire Length Length Of Wire Electric Current Key Factors Atoms Collisions Thickness Increases
Using these results, I can
now make a prediction as to what I should expect in the real
- Now that I have completed the experimental side of my
Investigation, I can use the results to explain if my prediction is
correct, and if not, why not.
- In electricity, the property that transforms electrical energy into
heat energy is resistance. A common factor that the entire conductors
share is the fact that they have free electrons in the outer shell of
their structure. Resulting from this, in all conductive atoms the
outer electrons are able to move freely, even in a solid (in this
particular experiment the Constantan wire).
- I predict that every time I decrease the length of the wire,
resistance will increase accordingly. This is because the longer the
conductor, the more particles there are in one way, resulting in the
electrons finding it difficult to flow. Also, as the length of the
wire is longer, this means electricity has further to travel, but
because it is in a longer wire, collisions will be less frequent.
- The Constantan wire is very thin: therefore there is a smaller area
for electrons to travel through. On their journey from negative to
positive, there are more and more collisions, giving energy to
- I know that as the resistance increases, the temperature of the wire
will rise. This is due to the fact the atoms in the wire are
oscillating faster. I believe the temperature of the wire is directly
proportional to the length and resistance.
- 100 cm ruler: to measure the wire accurately.
- 100cm wire: to experiment upon.
- 1 ammeter: to measure the current in the circuit.
- 1 voltmeter: to measure the voltage in the circuit.
- Connecting wires: to connect all necessary apparatus to the circuit.
- Crocodile clips: to connect the wires to the devices.
- 1 power pack: to supply AC current and control voltage.
- Collect all of the equipment and set up as shown in the diagram.
Make sure the ammeter is placed in series and the voltmeter inserted
- Set the wire to 100cm, and place two crocodile clips at the first
- Record the current in amps and the voltage in volts into the results
- Repeat the process from step 2, remembering that one crocodile clip
should always be placed on 0cm, with the other one moving up 10cm’s
- Continue doing this until all measurements up to 100cm have been
- Using results gathered work out averages of the current and voltage.
- Using the formula R=V/I, work out the resistance in ohms with a
Factors ensuring a fair experiment:
- Do not alter the positions of any of the devices during
- Record the current and voltage accurately, using correct units.
- Always place the crocodile clips on the exact measurement.
- Before beginning experimentation ensure all apparatus are fully
- Leave the voltage at the same level throughout the experiment.
- The wire must be straight as bends may affect resistance.
- The reading of the voltage should be taken promptly as when the
current passes through the wire, the wire will become hotter, but I
wish for heat to not play that big a role in my results.
- Keep the power pack voltage below 2V.
- Ensure all equipment is safe to use.
- If you smell burning, quickly switch off from the mains.
Current (I, amps)
Voltage (V, volts)
Resistance (R, ohms)