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How to write-up homework solutions

Doing homework is a critical part of learning physics, and writing up homework solutions is important in learning to communicate effectively in technical subjects. Clear communication can also aid in clear thinking. For every homework problem that is marked as “long-answer format”, we want a solution, not just an answer. The solution will have a style you've seen before in physics textbooks: equations interspersed with explanatory sentences. The sentences can be quite terse, but there needs to be verbalized logic. What you submit for grading should be a clearly presented solution that another student could learn from.

To help you learn clear and effective technical communication, the homework grade will be partially based on communication (20%) and partially based on content (80%). The rubric for this communication grade is outlined below. Worked examples in your textbook are another good guide to what is expected.

Remind the reader of your goal

Just like writing an essay, the long-answer format has a beginning, middle and end. At the beginning, there is a sentence (or two) reminding the reader of the goal. For example, “We want to find how much heat is leaking out of a typical house.” Feel free to use pictures/diagrams to help define the goal.

Use words to explain significant steps

“Significant steps” means “steps involving a new piece of physics or mathematical reasoning.” For instance, you might say, “We now apply conservation of energy” or “Using the Stefan–Boltzmann law…” If you make a mathematical manipulation such as changing variables in an integral, say so: “We now change variables to u ≡ 1/r.” If you invoke a result from your text, say something like, “Applying Equation (8-21)…,” and so forth. These short sentences will be interspersed throughout the mathematics of your solution.

Just a computer programmers put comments in their software code, physicists put comments explaining significant steps in their solutions.

Show all nontrivial steps

For a definition of a nontrivial mathematical step, be guided by model answers for the homework and worked examples in your textbook.

Comment on your answer

At the end of many homework questions there will be a specific prompt for sense-making. The response to a sense making prompt might be “An energy leak of 1000 J/s is consistent with the typical energy consumption of a household, 40 kWh/day”. Or, “This solution approaches the classical limit when the number of photons is large”. If the question does not explicitly ask for sense making, I still encourage you to find your own ways to make sense of the answer and include such comments at the end of your solution.


The pages you turn in for grading are something to be proud of, especially since you may have spent quite a few hours producing it. Homework will be run through a digital scanner, therefore all pages should be single sided. We prefer if you write you answers on blank white paper (8.5“ x 11”). It is OK to use ruled paper, but please skip lines occasionally to make your paper more legible and leave white space for the grader's comments. Avoid using grid paper, it is hard to read. Do not use red ink. Leave some space between problems. No more than two problems per page. Circle your answer. Include units whenever appropriate. Quote any numbers to the proper number of significant figures: no more sig. fig. than any of the input numbers.

wiki/homework.txt · Last modified: 2019/10/07 18:24 by ethanminot