EAT119 – Electrical & Electronic Principles
Laboratory 1 – DC Circuits
Introduction
This activity allows you to experimentally test and confirm your understanding of DC circuit theory
including: –
a) component recognition,
b) resistors in series (Kirchhoff’s Voltage Law),
c) resistors in parallel (Kirchhoff’s Current Law),
d) Maximum Power Transfer theorem,
e) circuit simulation using Proteus.
To complete this exercise, you will require the following items, which are available on request from
the technician who is based in room DG201: –
? 9 volt PP3 battery and battery clip (or a variable DC power supply)
? Single strand wire and wire stripper
? Pack of 4 resistors1
? Multimeter
1. Ten different resistor sets are available, and you must request the correct set, based on the last
digit of your student number, prior to the ‘/’. For example, if your number is 123456789/1 then you
should request resistor set ‘9’. These items must be returned in good condition after use.
FAILURE TO USE THE CORRECT SET OF RESISTORS WILL RESULT IN A MARK OF ZERO!
Task 1 – Resistor Colour Codes (10 marks)
Your resistor pack contains 4 resistors, consisting of three unique colour codes, but with two
resistors identically marked.
a) Use the resistor colour code to identify the stated value and tolerance band of each unique
resistor code (2 marks).
b) Measure the actual resistance of each resistor by using a multimeter (2 marks).
c) Create a table showing the colours of each band, nominal value, tolerance and measured
value of each of your resistors (2 marks).
d) Comment on whether your measured resistance values are within the stated tolerance, the
accuracy of your results, and any potential sources of error (4 marks).
Task 2 – Resistors in Series (Kirchhoff’s Voltage Law – 10 marks)
Use a prototype board to construct a series circuit with your 4 resistors, as shown.
a) Measure the actual EMF produced by the battery and the potential difference across each
resistor (V1, V2, V3 and V4) (2 marks).
b) Use your results from part a) to prove Kirchhoff’s Voltage Law (2 marks).
c) Calculate the total resistance of the circuit and then use Ohm’s law to predict the current
which would be expected to flow through the circuit (2 marks).
d) Connect an ammeter in series with the battery and measure the current flowing (2 marks).
e) Comment on your results and whether these agree with theory, and explain any differences
(2 marks).
Task 3 – Resistors in Parallel (Kirchhoff’s Current Law – 10 marks)
Use a prototype board to construct a parallel circuit with your 3 unique resistors2
, as shown.
2. Do not use the duplicate resistor for Task 3.
a) Measure the actual EMF produced by the battery (2 marks).
b) Connect your multimeter as an ammeter (i.e. in series) and measure the total current from
the battery ( ), and also the current flowing through each resistor ( , , and ) (2 marks).
c) Use your results from b) to confirm Kirchhoff’s current law (2 marks).
d) Calculate an equivalent single resistance which could replace R1–R3. Use this value to
calculate the expected total current, and compare this with the total current measured in b)
(2 marks).
e) Comment on your results (2 marks).
Task 4 – Maximum Power Transfer Theorem (10 marks)
Begin by constructing the above circuit, setting the source and load resistors to be your two
identical resistors.
a) Measure the battery voltage, the voltage across RS and RL and calculate the power dissipated
in each resistor (2 marks).
b) Replace the load resistor with each of your other three resistors, repeating the calculations
from part a) in each case (2 marks).
c) Comment on which load resistor allows the maximum power to be transferred, and the
efficiency of power transfer (2 marks).
d) Is ‘maximum power transfer’ the same as ‘maximum efficiency’? Explain your answer
(4 marks).
Task 5 – Proteus simulation (10 marks)
a) Create a Proteus simulation3
as evidence (3 marks).
b) Use your simulation to repeat the chosen activity, recording all simulation results and
repeating all calculations (3 marks).
c) Discuss your findings, commenting on whether they agreed with theory, and with your
experimental results, accounting for any differences (4 marks).
3. Proteus simulation software is available in areas E + F of the David Goldman Informatics Centre. A
Proteus user guide for DC Circuits is available on SunSpace.
Task 6 – Written Report (30 marks)
You must produce an individual word processed report which gives evidence that you have
completed all required activities. This must be submitted online through SunSpace by 11.59 PM
Friday 5th February 2016.
Marks will be awarded for: –
a) Appropriate report structure, use of language and style (10 marks)
b) Effective use of IT (10 marks)
c) Linking of experimental results with theory, supported by appropriate references (10 marks)
Task 7 – Electrical Health and Safety (20 marks)
As part of the practical you have been asked to give an overview of the current UK standards and
approved codes of practice that should be observed when working in the electrical laboratory. The
activities a student would be expected to carry out in the laboratory include using testing and
measuring equipment that is supplied by the mains power. Your overview should also include a
“Code of Practice” which gives brief instructions to users of the lab on how to comply with the
standards. This section of your report should be no longer than 500 words.
Marking Scheme
Resistor Colour Codes /10
Resistors in Series (Kirchhoff’s Voltage Law) /10
Resistors in Parallel (Kirchhoff’s Current Law) /10
Maximum Power Transfer Theorem /10
Proteus Simulation /10
Report Structure /10
Use of IT /10
Links to Theory, supported by References /10
Health and Safety /20
Total: ______ / 100
Appendix A – Circuit Construction Hints and Tips
Example Wiring – Series Resistor Prototype Board Circuit
Example Wiring – Parallel Resistor Prototype Board Circuit
Measuring resistance
The resistor must be disconnected from the circuit before attempting to measure resistance.
Measuring Voltage and Current
Voltage may be measured by connecting the meter in parallel with the chosen component. Voltage
is measured while the circuit is ‘live’. (The voltmeter has a very high internal resistance so should not
affect the circuit.)
Current is measured by connecting an ammeter in series with the component whose current is to be
measured. Current is measured while the circuit is live. (Caution: The ammeter has a very low
internal resistance and will be damaged if it is connected in parallel, unlike a voltmeter.)