How to Write a Physics Lab Report

...and hopefully get an A+!!

General Guidelines Don’t make it dense

Main point is to communicate your results

Know what it is expected of you

Read the lab and do your pre-lab

Listen during lab talks!

Introduction Section Type of Report

Formal Short Purpose* Theory* Method*

Apparatus Procedure

Observations Calculations & Errors

Graphs Results

Discussion & Conclusion

Prelab Do it!

Written before attempting the experiment

Usually ‘purpose’ and ‘method’ sections

Sometimes ‘theory’

Good idea to prepare tables with headings (but leave them open ended)

Purpose

The purpose of this slide is to clarify what the purpose of your lab should contain.

The purpose is a clear statement of the scientific objective of the experiment.

Usually just one sentence.

Be clear. Be direct.

Theory** Background information

Theoretical justification of the experiment

In conjunction with the ‘method’ section, it should make the experiment comprehensible

A brief discussion of the physics of the phenomenon leading to a statement of the theoretical equation

The equation should be explained and all variables should be defined

Method** Done in conjunction with the ‘theory’

General terms without going into the procedure

How the experiment will be carried out

How the data will be analyzed

How the theoretical equations are manipulated

Variables in the equation are rewritten with actual quantities which will be observed

Apparatus** A diagram of the apparatus (sometimes - if it improves clarity) with its essential features and geometry

The serial number, size, or other identification of the instruments

The range and precision of all measuring devices

All circuit diagrams (these also need to be given in short reports!)

Procedure** Past tense and passive voice of how you carried out the experiment (no point form!)

Usually written up after the experiment

Details of what you actually did

Special precautions you took to deal with problems of execution

Don’t copy the lab manual!!

Also account of which quantities were read, which points were redone and why

Observations Copy down anything you see

Use TABLES when you can to keep your data organized and easy to read!

Put headings in your table with the errors

Calculations Calculations using your measurements

Use the formulas from your methods section to calculate the wanted value using your measurements

Calculate the error on all your values

Ensure proper significant figures

Ensure proper units on all values

Average value calculations: Xavg= (x1 + x2 + xi…./ number of x values)

Error Calculations Random error:

Standard Deviation on a value (∂x)= [(∑Ni=1(xi-xavg)2)/(N-a)]1/2

68% of the occurrences of x (measured value) should fall within the range (x-∂, x+∂)

The standard deviation can then be used to find the uncertainty on a MEAN X value: ∂x(avg)= (∂StD)/√N

Above the ∂x(avg) is the uncertainty on the average X value or “Mean X”, and ∂StD is the standard deviation on the x value.

You write this result as: X ± ∂x(avg)

Analyzing Data Analyzing your data:

•Inefficient Statistics: ∂ineff=(H-L)/ √N

•H=maximum value

•L=minimum value

•N=number of values

•How to choose between the Standard Deviation of the Mean value ∂StD vs. Reading Error value (RE) when evaluating the experimental error on the average of a set of data. Use this table as a guideline:

• ∂StD < 2 x RE ∂StD ≥ 2 x RE

• Use RE Use ∂StD

Comparing Results

Consistency Test:

• ∆= |x2-x1| ∂∆=√(∂2 x1 + ∂2x2)

• (∆/∂∆) ≤2 Consistent Results!

• (∆/∂∆) ≥ 2 Inconsistent Results!

Results

Clear statement of the experimental results as they satisfy the objectives stated in the purpose

Give the units of the results

Include the estimated errors

Use the correct number of sig figs

Discussion and Conclusions

Critique of the experiment

Nothing new should be introduced in this section

Based on data and qualitative observations

Considerations growing out of the data analysis

Results should be compared with known values in the literature (when possible)

Consistency should be compared and commented on

Changes which could improve precision of the procedure

Possible sources of error

Hints..

Talk to your TA - get to know them and their preferences

Read their comments

Apply those to your next lab

Ask questions EARLY

Utilize your resources