EAT118 Electrical Laboratory Exercises – Inductance and Capacitance Task 1 – Inductance of a Solenoid
EAT118 Electrical Laboratory Exercises – Inductance and Capacitance
Task 1 – Inductance of a Solenoid
Your objective is to investigate the equation which describes the inductance of a long thin solenoid:
Where is the number of turns, is the average cross sectional area (m2
), is the length (m), is
the permeability of free space (
) and
is the relative permeability.
Equipment Required
For this exercise you will be provided with the following materials:
? An iron nail
? A length of enamelled (insulated) copper wire
? A multimeter capable of measuring inductance, resistance and capacitance (LCR meter)
? A ruler
? A small piece of sandpaper (to remove enamel insulation)
Inductor Construction
Begin by wrapping the wire around the nail, as shown in Appendix A, carefully counting the number
of turns. (Use the table below to identify the required number of turns based on your student
number).
Table 1: Number of required turns of wire, based on your student number
Last digit of your student number Number of required turns of wire
0 60
1 65
2 70
3 75
4 80
5 85
6 90
7 95
8 100
9 105
Method and Analysis
Connect a suitable LCR meter and measure the inductance, as shown in Appendix A, Step 7.
Use a ruler to measure the length of the coil ( ) and the average diameter, converting all lengths to
metres. Calculate the cross sectional area ( ) – which is based on the equation for the area of a
circle.
Rearrange the inductance equation to make
the subject and then calculate the value of relative
permeability
. Compare your result with that expected, assuming the nail is made from iron.
Vary the length ( ) of your inductor by stretching or compressing it, noting the effect on the
inductance. Create a table showing the variation of inductance with length and plot your results on a
graph. Compare your findings with that expected, based on the inductance equation.
Task 2 – Capacitance of a Parallel Plate Capacitor
Your objective is to investigate the equation which describes the capacitance of a parallel plate
capacitor:
where is the capacitance (F), is the area of the plates (m2
), is the
permittivity of free space,
is the relative permittivity and is the distance
between the plates (m)
Equipment Required
For this exercise you will be provided with the following materials:
? Aluminium Foil for the conducting plates
? Dielectric material (either greaseproof paper or plastic film may be used)
? An LCR meter or multimeter capable of measuring capacitance
? A ruler.
Capacitor Construction
A simple parallel plate capacitor may be created using two sheets of aluminium foil, separated by a
sheet of suitable dielectric material (greaseproof paper or plastic film). See Appendix B for details of
capacitor construction and capacitance measurement.
Experimental Method and Analysis
During the lab session you should do the following:
1. Create a range of capacitor sizes with different values of area ( ) for a fixed value of plate
separation ( ).
2. Choose one of your capacitor sizes and vary the distance between the plates, hence
increasing the plate separation ( ) for a fixed plate area ( ). This may be achieved by placing
the aluminium sheets between the pages of a book.
For each capacitor you should carefully note all dimensions, measure the resulting capacitance,
and record this information.
Plot graphs to show how the capacitance (C) varies with area (A) and with plate separation (d).
Choose one representative set of data and calculate the relative permittivity, er
, of your chosen
dielectric. Compare your result with that expected for the chosen dielectric material accounting for
any differences.
Report
You should write a report detailing the results from both experiments. Your report should contain
the following information:
? A brief description of your experimental method followed for each task.
? Tables containing any data you have collected.
? Graphs relating your findings to the appropriate equations.
? An explanation of how you have estimated the relative permeability and relative permittivity
for the inductor and capacitor respectively.
? Comments on the effect of varying circuit parameters, comparing these with the expected
results according to theory.
? A brief discussion of potential sources of experimental error, and how your analysis
technique minimises these.
Mark Scheme
Data Collection
Description of Method /10
Evidence of Correct Data Collection /10
Identification of sources of Experimental Error /5
Data Analysis
Explanation of Method of Analysis /10
Estimated values of relative permeability / permittivity /10
Report Presentation
Graphs /5
Tables /5
Overall Presentation /5
TOTAL: /60
Your report should not exceed 7 pages. References are not required as the report is primarily
focussed on your own work. You may, however, use and reference external materials if you wish.
This electrical lab work contributes 25% of your overall mark.
Hand In Date:
This report should be submitted through SunSpace DropBox by 11:59 PM on Friday 15
th January,
2016.
Appendix A – Inductor Construction and Inductance Measurement
Step 1: Bend the first end into a loop, leaving about 5 cm of wire for the first connector. Pass the
second end of the wire through the loop in the direction of the arrow.
Step 2: Pull the loop tight, then begin winding the wire tightly around the nail in a clockwise
direction, keeping a count of the number of turns. (The required number of turns is given in Table 1.)
Step 3: Form a second loop after winding the required number of turns.
Step 4: Pass the remaining wire through the loop in the direction of the arrow and pull tight.
Step 5: Trim off the unwanted wire, leaving two connecting leads approximately 5 cm in length.
Step 6: Use sandpaper to remove the enamel from the leads, allowing electrical connection using
crocodile clips.
Step 7: Connect the meter as shown and read the inductance.
Appendix B – Capacitor Construction and Capacitance Measurement
Step 1: Cut out two rectangular pieces of aluminium foil. Cut out a slightly larger piece of
greaseproof paper, placing this between the two sheets of aluminium foil.
Step 2: Arrange the layers so the conducting surfaces are not touching. Connect the LCR meter using
the crocodile clip leads.
Step 3: Configure the meter as shown. Use a book or similar to apply even pressure and reduce the
separation between the plates. Read the capacitance from the meter.