I will usually be available for questions on any given day for an indefinite period following class (usually 1-2 hours, but I'm happy to make "office hours" extend over most of the afternoon if that is necessary). We'll schedule homework in such a way that you have at least one day to ask me questions or for help on any homework problems you are having difficulty with before you actually have to hand it in.
You can always contact me via email at rgb at phy dot duke dot edu, and usually I will get back to you in a matter of seconds to hours. If something is urgent, feel free to call my on my cell phone number: 919-280-8443. However, note well that this is my cell and will interrupt whatever I'm doing at the time, so please don't totally abuse it in the evenings or at night when we're not having a viewing. You can always send me a text message asking for a contact or leave a voicemail message if I don't pick up right away.