Considerations When Serving on Thesis Committee I am part of a masters student's thesis committee for the first time in my career, and am unsure what I should be doing be during the question session following the public presentation.  I have read the whole document and have made comments about edits and corrections I would like the student to make, and have prepared a list of questions I could ask the student.  However, I am unclear on a few things:


What criteria should I use to evaluate the student's work?  What is necessary to consider their work good enough to pass? 
If there is a disagreement among committee members, how does that typically get resolved?
What should my goal be with the questions I ask?  I am already familiar with the theory and experimental design of the student's project, and could easily find myself digging into details or trying to test the student's overall knowledge of the field, but I'm not sure these would be useful ways to spend time. As the most junior person on the committee I expect I will be last, and unsure how much I'm expected to contribute to the examination.


For background, the student is at a different institution than I am, and my department does not have graduate students. We're both in the same city in the United States. I have talked to the student's advisor about the project itself, but I haven't gotten a clear sense of what I should be doing in the exam. The student's institution only lists administrative requirements for scheduling and submitting documents on their website, and doesn't seem to provide guidance for the contents of the thesis.
Internally within the committee, asking the committee chair is the best option. The chair should be able to fill you in with the procedure and what kind of angles the questions usually take. Be aware that the chair may still insist that you should decide what kind of questions to ask. And from my experience serving in committees, they did mean it.

Externally, since your institute is in the same city with the host, why not go attend a public defense there? That way you can also get the tone right. Do know that, however, tone/attitude can still vary greatly within an institute.

As for what to ask... first, I'd say don't ask any structural questions that would destroy the student's work. Those should be cleared up before the committee signed off the student to present. Second, unless it's for clarifying some question in the results or data, use open-ended questions. From my experience, I usually ask 1-2 clarifying question (e.g. on a limitation they suggested, etc.) and 1-2 "what if's" (e.g. what would you have changed if you can redo this work?) or "how should this work be carried forward", etc. That's just my style, I like to start by making it feel like the candidate is a student answering questions to end with treating the candidate as a new expert who can make recommendations and broad takeaway.