Writing a lab report

Lab report purpose

Whatever branch of engineering you are studying, many of your labs and lab based assignments will require a written report. The purpose is to report what you did and what you learned from an experiment.


Lecturer's advice

The marker is looking for evidence that you:

  • understand what happened, why it happened and what it signified in relation to the experimental aims
  • can structure and present your lab report logically in accordance with established conventions.

Lab report structure

Lab reports can vary in length and format. These range from a form to fill in and submit before leaving the lab, to a formal written report. However, they all usually follow a similar basic structure.

MEASUREMENT OF THE FRACTURE TOUGHNESS OF PERSPEX

A. Student

Abstract

Perspex samples with sharp and blunt cracks were subjected to loads to determin fracture toughness. Results clearly show a correlation between...

Aim

To determine the fracture toughness of Perspex.

Introduction

Fracture toughness is a measure of the fracture resistence of a cracked material. The two types of crack investigated here are shown in Figure 1. For a sharp crack to propagate...

Method

Six Perspex samples with artificial blunt cracks of various sizes were supplied. The samples were secured into the micro-tester and the strain rate and maximum load parameters set to...

Results and Discussion

The six specimens were tested to three loads and the corresponding deflection calculated. The average compliance at each crack length was calculated; these are plotted in Graph 1. The calculated exponent is close to the quadratic relationship...

Conclusions

The experimental results show that fracture toughness decreases with increased crack length and velocity...

Activity

The typical structure of a lab report is shown in the left-hand column below. Can you match the sections with their description? Drag and drop the descriptions in the right-hand column to the section it matches.

Click on the links below to find out more about the different sections of a laboratory report.

Title

Abstract

Aim

Introduction or Background

Method

Results and Discussion

Conclusions

Appendices

Title

ENG3051 Week 5 Laboratory

Chromatographic separation of protein molecules

A. Student 10203040

B. Learner 90807060


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Abstract

Also called the Summary, this section gives an overview of the full report. It tells the reader:

  • What you did: the aim of the experiment
  • How you did it: a brief description of the method used
  • What you found: your results and how you interpreted them
  • What it means: what your results mean in relation to the aim.

There is no need to include background information such as motivation or theory.

Example:

In this experiment a wind tunnel was used to measure the lift and drag forces on a 1:70 scale model of an aeroplane in order to determine the optimal angle of attack. Angles of attack ranging from -8° to 20° were tested at a wind speed of approximately 30m/s. The typical pressure distribution  around an aerofoil at small angles of attack was found to be low on the upper surface and high on the lower surface, creating an upward lift force. As the angle of attack increased, so too did the lift force exerted on the plane from the aerofoil wings. However, there is an optimal angle of attack after  which the lift will begin to decrease. This is because increasing the angle of attack also increases the drag on the aerofoil. An 8° angle of attack was found to be optimal.


Identify the features of an Abstract – what you did, how you did it, what you found and what it means in relation to the aim – in the sample above. Consider how much attention is given to each. Then answer the True or False questions below:

Activity

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Aim

In any experiment, you aim to do something. For example, to verify, to investigate, to measure, to compare or to test a hypothesis.


Writing tip

  • Use the verb form starting with 'to' (e.g. 'to investigate').
  • Avoid the noun form (e.g. 'investigation') which is better suited to the title.

A single Aim should be written in a complete sentence.

Example 1:

AIM
The aim of the experiment is to determine the resistivity of iron by measuring the resistance of a specimen of wire.


Lecturer's advice

Consider how you will know when you have achieved your aim. This should be apparent from your aim statement. In the aim statement above, it is clear that the aim will be achieved when a value is obtained for the resistivity of iron.

If an experiment has more than one aim, list them in the logical order.

Example 2:

AIM
1. To measure the pressue distribution around a cylinder in a wind tunnel
2. To calculate the forces on the cylinder based on the data obtained


Writing tip

Where there is a goal-and-means relationship, make sure this is clear.

bad Aim A:

  • To conduct lift and drag measurements on a scale model aeroplane
  • To assess the behaviour of a full-scale aeroplane under three hypothetical conditions.

good Aim B:

The aim of this experiment is to conduct lift and drag measurements on a scale model aeroplane and use the results to assess the behaviour of a full-scale aeroplane under three hypothetical conditions.

In Aim A above, the relationship between the two parts of the experiment is not made clear.


Writing tip

Writing concisely will help you convey exactlywhat you want to achieve in the experiment.

Activity

Compare the two (Aim) statements below:
AIM A To conduct lift and drag measurements on a model aeroplane in a wind tunnel.
AIM B To measure the lift and drag forces on a model aeroplane in a wind tunnel.

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Introduction or Background

The Introduction (sometimes called Background) should:

  • introduce the topic and purpose of the experiment
  • explain the relevant theory in detail, including relevant laws, equations or theorems
  • indicate the method/s you will use for analysis, such as nodal analysis, numerical modelling or microscopy.


Lecturer's advice

Provide enough background that the reader will understand the experiment without having to refer to the lab instructions.

Always write the Introduction in your own words; don’t just copy from the lab notes.

Example:

Introduction

The use of solar water heaters is rapidly increasing in both homes and businesses as they provide an environmentally friendly and cost effective source of energy. However, significant improvement to their heating efficiency is required before they can be used without  a  supplementary    energy source. This experiment investigates two factors affecting the heating efficiency of solar water heaters: mass flow rate and collector design. Firstly, the efficiency of a flat plate collector (Figure 1) is examined by measuring the temperature of the absorber plate, insulation  and  water    at various flow rates using a rotameter to control the rate of water input into the collector. Secondly, two different methods of welding the water tubes to the absorber plate are tested…


The Introduction can include any figures, tables or equations necessary to explain the relevant theory. It should also set out any assumptions, and indicate how the data will be processed. Always cite your sources of information, including your lecture notes.

Example:

Example of a lab report equation defining the thermal efficiency of a solar collector

Solar lamps will be used to model the incident radiation received by solar heaters from the sun. However, it is not possible to reproduce the uniform radiation flux at the surface of a real collector. Therefore the average radiation flux at the surface of the collector will be used in calculations.

It is always best to draw figures yourself if you can. If you do use figures from another source, indicate in the citation whether you have modified it in any way.


Method

This is where you describe what you actually did. This includes how the data was collected, any experimental difficulties you encountered and how you resolved or overcame them. If any aspects of the methodology are likely to contribute systematic error to the data and results, point this out in sufficient detail in this section.

Materials and/or Experimental setup

Begin with a description of the materials used and/or the apparatus setup accompanied by:

  • an image showing the relevant features of any object or material under investigation
  • a diagram of the experimental setup, with each component clearly labelled

This experiment required a particular apparatus setup.

Example 1:

The performance of a flat plate solar collector was analysed using a small scale test rig. The rig was as shown in Figure 3, with the exception of the water pipes (see Figure 4). Thermocouples were connected to the collector as shown in Figure 3, and attached at the inlet and outlet of the water pipes  to    measure ambient temperature.

Theormocouple figure

Figure 3. Flat plate solar collector setup

Figure 4. Wired joint

Figure 4. Wired joint


This experiment required material to be prepared in a particular way.

Example 2:

The samples were prepared by cutting square tiles with side lengths of ~5mm from a 1mm x 50mm x 50mm sheet of 99.9999+% (6N) pure aluminium, purchased from Company X (see appendix for a chemical assay). The tiles cut from this sheet were then mounted onto glass microscope slides with thermal wax  in order to provide sufficient support and for ease of mounting into a wire saw.


Procedure

When you carry out an experiment, you usually follow a set of instructions such as these which may include extra information to guide you through the steps.

Example lab handout:

Week 5 Laboratory instructions

Aim: This week we calculate and analyse the stoichiometry of bicarbonate decomposition.

Procedure

  1. Initiate the bicarbonate feed pump and adjust the flow rate to 230mL/min. Wait until the flow rate has stabilised before proceeding.
  2. Admit cooling water to the condenser at maximum flow rate. The liquid seal will fill and overflow, so that steam enters the reactor.
  3. Increase steam pressure gradually until…

When writing up the Procedure, you must report what was actually done and what actually happened, omitting any extra information such as helpful hints included in the instructions. This experiment might then be reported as follows.

Example 1:

The flow rate of the feed pump was set to 230mL/min and cooling water was added to the condenser at maximum flow rate. Once the steam had overflowed into the reactor, the pressure was increased to…


Lecturer’s advice

You need to include enough detail for someone else to replicate what you did and get a similar outcome. You should also explain any extra actions or decisions made during the experiment.

Example 2:

The rotameter was adjusted each time by the same member of the group in order to ensure consistent readings.

Writing tip

In the Procedure section you should use:

  • the past tense because you are reporting on a past activity
  • the passive voice when reporting what you did.

The pressure was increased until the steam overflowed into the reactor.

Increase the pressure until the steam overflows into the reactor

❌ This is an instruction, probably copied from the lab handout.

We increased the pressure until the steam overflowed into the reactor.

❌  The traditional view is against using ‘I’ or ‘we’.

✔ But some lecturers don’t mind if you do - check to be sure.


  • The main reasons for using the passive voice are:
    • If the subject of the sentence (i.e.: who or what performed the action) is not known or not relevant. E.g.; Annealing is used to soften metal for shaping.
    • To avoid starting every sentence with “I” or “We” when describing what you did.
  • In all other cases, use the active voice.

After three minutes the steam overflowed into the reactor.


Read the lab handout below:

The effects of surface roughness on drag force

Equipment

Cylinder - 2408mm high, 80mm diameter

Wind tunnel working area: 304.8mm x 304.8mm x 812.8mm

Procedure

1. Choose a way to apply temporary rough surfaces to the cylinder. Your chosen method must be able to simulate at least two noticeable variations in surface roughness.

2. Calibrate the strain gauge and record a zero reading. You can find the calibration coefficient by applying known masses to the model. The results can then be plotted to determine the calibration factor.

Activity

Now read the two student lab reports below and answer the three questions that follow. Scroll down and use the blue dots or arrows to move to the next question.

Group A report

The effects of surface roughness on drag force

Procedure

After a long discussion our group chose sandpaper to simulate variations in surface roughness as there is a big difference between the lightest and heaviest grades. To make sure the sandpaper wouldn't come off under high wind velocities, we came up with the idea of sticking it to the cylinder with double-sided tape. We found the calibration coefficient by applying 4 known masses to the model and plotting the results.

Group B report.

The effects of surface roughness on drag force

Procedure

It was decided that sandpaper would be the most effective  way to simulate variations in surface roughness due to the significant variation between the lightest and heaviest grades. Because the sandpaper will be subjected to very high wind velocities, in order to make sure that it will not be dislodged in the wind tunnel, it will be wrapped around the cylinder and secured with double-sided tape. Before beginning, the strain gauge must be calibrated to obtain a zero reading. The calibration coefficient is found by applying four known masses to the model and plotting the results.


Lecturer's advice

Never copy and paste from the lab handout; report on what actually happened.

In some cases, you may be allowed to direct the reader to the standard followed or to the relevant page of the lab manual.

Example:

The experiment was carried out according to the instructions on page 23 of the CHE2202 Lab Manual.


However, only do this if you are completely sure it is permitted and clearly describe any deviations from the instructions.

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Results and Discussion

In this section, you present your processed data in graphs, figures or tables and explain their significance in relation to the experimental aim. This usually involves comparing them with the calculations made in your preliminary work or the published theoretical values.


Lecturer's advice

If you have a long set of complex results, it may be more appropriate to present them in one section called Results, and discuss them in a separate Discussion section. However, moving back and forth can be confusing for the reader. The objective is to tell the story as simply and clearly as possible.

Presenting results

  • Present your processed data in graphs or tables.
  • Explain how the raw data was processed to obtain the final results.
  • Include an error analysis where applicable.
  • Provide sample calculations for each step of the process in an appendix.
  • When the process need only be carried out once, include the working here rather than in an appendix.

Present your data in graph or table form so that it is easy to compare your results with the expected values

Example table labelled as "Table 1. Circular cylinder data". Tables are labelled above the table. Unites are given in the column headings

Sample graph labelled "Figure 3. Lift and drag co-efficients at various angles of attack". Figures are labelled below. Label both axes including units. Provide a key to symbols.

Microscopic image labelled "Figure 4. Scanning electron micrograph of the surface of an AI-Si-Ge alloy illustrating Si-Ge core-shell particles on the surface of the material". Provide magnification value for microscopic images. This can be included as part of the caption. Figure titles should state what the figure is and what it contains.

Numbering

  • Tables are referred to as Table 1 etc, numbered sequentially.
  • Everything else (graphs, images, diagrams etc.) is referred to as Figure 1 etc.

You must refer to every figure and table in your text, so that the reader understands the content and purpose of each. Explain clearly how you obtained final values, and tell the reader where to find raw data and sample calculations.

Example 1

The drag and lift coefficients for the model aeroplane are shown in Graph 3 below. Sample calculations are presented in Appendix 4.


Example 2

Part 1

Six specimens of Perspex were tested to three loads (see Appendix 1) and the corresponding deflection calculated. The average compliance at each crack length was calculated and is plotted in Graph 1. To calculate the fracture toughness of Perspex the derivate ofwith respect to a is required. Linearizing Graph 1 allows an expression between compliance and crack length to  be modelled. The linearized relation form of the relationship allows the power law relationship to be determined.
Image showing the calculation of fracture toughness of Perspex using equations


Discussing results

This is where you:

  • comment on the results you obtained
  • interpret what the results mean in relation to the aim of the experiment
  • explain any unexpected results.


Lecturer's advice

Your marker wants to know how well you understand what happened in the experiment. You should:

  • identify and comment on trends
  • compare the expected and experimental results
  • identify any sources of error in your measurements
  • suggest explanations for unexpected results
  • where appropriate, suggest how the experiment could have been improved.

Example 1:

Varying the angle of attack in the positive direction increased the lift until the wind reached an angle of attack of 10°, after which it decreased. This is consistent with the standard trend [3].


Example 2:

The values found for the pressure coefficients around the cylinder (graph 5) are consistent with the accepted trend for laminar flow (graph 6). The sudden increase in the pressure coefficient at 190° is due to the cylinder becoming dislodged from its position perpendicular to the flow.

When discussing your results, begin by directing the reader to the relevant table or graph.

Sample report

The rotameter calibration results are shown in Table 1, and the corresponding mass flow rates plotted as the calibration curve in Figure 3. The results appear linear with no significant outliers, suggesting that the rotameter is an effective way to control the water flow rate.

Tips

1. Begin by directing the reader to the relevant figure, table or graph. This is called a location statement. It tells the reader where to look and what to focus on.

2. Then explain what the results mean in relation to the experimental aim.


The example below, from an experiment measuring the saturation pressure of water, shows the main features of a Discussion.

Example of Discussion

Activity

The paragraph below contains some, but not all, of the functions of a Discussion. For each sentence, select the appropriate function or functions from the following quiz.

Example:

Figure 5 shows the standard efficiency curve for each of the two collector types investigated. While the data points for the formed fully soldered joint are significantly spread out from the line of best fit, the soldered joint data points lie close to the best-fit line. The latter indicates a strong similarity to standard efficiency curves given in Hessami (2006). Both best-fit lines indicate that efficiency increases with reduction in water mass flow rate, which is characteristic of standard efficiency curves.

The efficiency of the solar collectors could be improved by the use of one-way glass to reduce incident radiation losses due to reflection, as well as by better insulation of the experimental apparatus.

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Conclusions

This section summarises the key results and discussion points.

  • Indicate to what extent the aims of the experiment were achieved.
  • Summarise the main points of your findings including key values.
  • Summarise important limitations and the cause of unexpected results.
  • Recommend improvements to overcome experimental limitations.


Lecturer's advice.

Your Conclusion should answer the question: So what? Students often write weak conclusions because they do not put sufficient emphasis on the significance and relevance of their results in relation to the Aim of the experiment.

Example:

Aim
The aim of this experiment was to compare the effect of two different collector designs and variations in water flow rate on the performance of a flat plate solar collector.
Conclusion
Experimental results showed a clear correlation between the collector efficiency of a solar water heater and water mass flow rate. The most efficient of the two collector designs tested was the formed fully soldered joint, due to the greater contact area between collector and  pipe  maximising heat transfer to the fluid. The optimal efficiency point obtained for this design was at the highest water mass flow tested, 0.095kg/s, suggesting that the actual optimum may be higher. It is therefore recommended that a higher range of flow rates be tested. The data also suggests that  an  efficiency of over 80% is achievable, and significantly greater than the currently accepted maximum.

Activity

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Appendices

These contain material that is too detailed to include in the main report, such as tables of raw data or detailed calculations.

  • Each appendix must be given a number (or letter) and title.
  • Each appendix must be referred to by number (or letter) at the relevant point in the text.

Example:

The calculated values are shown in Figure 3 below. For detailed calculations, see Appendix 1.

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This tutorial has presented the basic principles of writing lab reports. However your lecturers may specify small variations in structure or style. Always check your assignment instructions carefully.