Quoting from the VT ECE Graduate Student Policy Manual:

"The Preliminary Examination is normally taken near the end of Ph.D. course work. This is an oral exam, before the student’s advisory committee that determines the student’s ability to develop scholarly research. The student presents the results of his or her current research investigations along with an outline of a proposed Ph.D. dissertation. The examination committee may also ask questions on course work and related topics, including possible written, open-ended questions prior to the oral exam."