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.