Of the ammeter and voltmeter respectively. Repeat the procedure using eight
Different lengths ranging from 10cm to 80 cm. Then, repeat the same experiment
Two more times to get an average.
CALCULATING THE RESISTANCE
The formula for calculating the resistance is: Resistance = voltage/current (V/I)
CALCULATING THE AREA
Using a micrometer screw gauge, measure the diameter of the wire at four different
Points and at right angles of each of these points and get an average. Then calculate the area
With the formula A=πr
Where r is radius=1/2 diameter
A is area
π Is 22/7
APPARATUS
A digital ammeter of range 0-20 A, a digital voltmeter, which ranges from
0-20v, positive and negative terminal blocks, available power supply box,
A meter rule of 1 – 1000mm graduation, a micrometer screw gauge and a
Piece of constantan wire.
SAFETY PRECAUTIONS
Do no touch the wire when the power supply box is switched on
Do not cut yourself while cutting wire
Be careful not to start a fire by allowing the wire to overheat
Be generally careful and safety conscious during the experiment
After plotting the graph, calculate the gradient with the formula
G= y2-y1 = y
X2-x1 x
After finding the gradient
R= ρA
L
To calculate the resistivity (ρ) make ρ the subject of the formula
ρ = RA
L
IMPLEMENTING
To calculate the area of the wire, measure the diameter at 4 different points and
At angles of each point
0.46mm+ 0.45mm+ 0.46mm + 0.47mm
1.88mm = 0.46mm
4
r = 1 d = 0.46 = 0.23
- 2
PRELIMINARY EXPERIMENT
During the preliminary experiment,
I observed that the resistance of a piece of wire is affected by the length and the
Area * the longer the wire the greater the resistance RαL
* The fatter the wire, the less the resistance RαL/A
I observed that as the voltage increased, the current decreases, which means that
The current is inversely proportional to the voltage. Infact as the wire is an Ohmic
Conductor, the result from the graph can be plotted an I-V graph. An Ohmic conductor
Should yield a straight-line graph passing through the origin.
MAJOR SOURCES OF ERRORS
Human errors
Parallax errors
Kinks and twists on the wire
Change in diameter due to change in temperature
ACTIONS PROPOSED TO MINIMISE ERRORS
Keep the area constant as much as possible by trying to keep the temperature
Constant at all times. This was done by switching the power supply box each
Time you take a set of result to let it cool down for a while before switching it
On to record another set of results. Also keep the area constant by using the same
Piece of wire throughout the experiment.
Try to avoid parallax error by using a digital ammeter and voltmeter instead of a
Full-scale deflection ammeter and voltmeter.
Ensure that the wire is carefully tightened to both ends of the meter rule and avoid
Wires with loads of twists, which could alter the length and cross-sectional area
Of the wire.
To increase the decree of accuracy of the recorded result and plotted graph, take
Three sets of results and calculate the average, even when calculating the area.
Record the diameter at a minimal of four different points to be able to measure
The diameter of the wires accurately as possible.
Use terminal blocks instead of crocodile clips because the crocodile clips kept
Slipping out from each other and disturbing the circuit. These terminal blocks
Make it easier to connect the circuit properly, but on the other hand, they make it
Difficult to measure the length accurately using a meter rule, so use larger length
So this inaccuracy is almost negligible.
Finally try to avoid normal human errors as much as possible by being generally
Careful.
The recorded results of the voltage and current flowing through the circuit
Resistance=voltage
Current
ANALYSING
After plotting the graph of length against the resistance, calculate the gradient, m,
With the formula
M= y2-y1 =Δy
X2-x1 Δx
=44.2 – 0.40 = 4.02
0.80 – 0.06 0.74
= 5.43
The gradient = 5.43
AREA: πr where r = 0.23
πr = π(0.23x 10 )
= 1.06 x 10
with the gradient ,m , I can now calculate the value for resistivity of constantan
wire.
R=ρL ρ=RA
A L
The formula for a straight line graph, y=mx and here,
ρ = R A
L
ρ= y, m= R/L, x = A
ρ = mA
= 5.43x (1.060x 10)
=5.75 x 10
CONCLUSION: At the end of my experiment, the resistivity of constantan wire
Is 5.75 x 10
EVALUATION:
The anomalies seen in my results (graph) were as a result of approximations. After I calculated the resistance, I approximated the result in order to be able to insert the numbers on my graph sheet and this affected my graph (gradient) because when
I plotted the graph without approximating; I got a perfectly straight-line graph.
Conclusion: I feel my experiment (practical) went well and was suitable for the
Task given. This is shown by the fact that I achieved consistency and proves that
This experiment can be both reliable and accurate. My result is reliable as they are consistence with each other and I have managed to refrain from making large errors.
Calculating the percentage error:
=5.75 x 10 – 5.2 x 10 x 100
5.2 x 10 1