Thursday, April 19, 2012

Students should write their own formula sheets

With in class exams there are several options on what access to background material that students should have:

1. Students can bring any material (texts, notes, assignment solutions).
2. Students can just bring a copy of the text without annotations.
3. Students can bring a one or two page sheet of formulas that they write themselves.
4. The lecturer provides a formula sheet.

Which do you favour?

1. Provides the most realistic "real world" type of assessment, but it can be hard to write new and suitable questions. Given the choice very few students will choose this option.

I have used 2. before. I found it surprising (and disappointing) that I could set questions whose answer could be found in the text but there were still a significant fraction of students who could not do them.

I have been using 3. lately for my solid state physics class (4th year undergraduates). The students hand in their formula sheets with their exam answers. I suspect I started doing this partly to reduce my workload and I thought it would be good revision exercise for the students. However, I am discovering that it is quite revealing to look over the student sheets to see what students do and don't include. Some are very well prepared and others are not. Some don't include fundamental constants they will need and then try to use this as an excuse for not completing a question.

The student sheets give an idea of how hard it is for students to identify key pieces of knowledge. Some equations are of tangential relevance and key ones are omitted. For example, in a recent exam only 1 out of 7 included Bloch's theorem in their formula sheet. Surely, this is the most important equation in the whole course! This underscores to me that we have to not just tell students what the key facts and concepts are but also (somehow) train them to be able to recognise what is really important.


  1. If you let students bring a textbook to an exam, that will be the first time some of them read it.

    I agree that letting students bring what we've written ourselves is the best option.

    I've never been a fan of a formula sheet being provided. It makes it seem like physics is about formulae. In some sense a formula sheet for an EM exam should consist of exactly five equations, since everything else is derivable from those (assuming that you give standard things like linear polarisability in the question statement, since it's an assumption about a material rather than something fundamental to the subject). However, that won't work for a real test. If students can write their own, it should be able to be more of a map to help remember the path covered in the course, and less "these are isolated equations to be applied without context to answer the questions".

    I would prefer to have a list of constants even if students provide their own formulae, because if you leave one off accidentally you can't "work it out" no matter how well you understand concepts, whereas a well-prepared student should be able to for most equations.

  2. I have always been a fan of writing one's own cheat-sheet. You do a huge amount of study in the actual writing of it, and as you rightly point out, it teaches you to recognise important equations.
    That said, I know most people write out virtually everything there is to the course in tiny writing (this is doable with a thin mechanical pencil and a double-sided A4 page), so this recognition is obviously dependent on writing size.

    Still, the act of creating a cheat-sheet brilliantly illustrates to the student what they do and do not know.