After you have finished a successful career here at the University of Minnesota, you are likely to consider applying to graduate schools. At present, this is an excellent choice since the number of undergraduates earning bachelor's degrees in physics is at the lowest point since 1960, the beginning of the space age, and so there are many good openings available to high-quality students. It is usually the best strategy to apply to a number of different graduate programs of varying degrees of quality, so that you can get into the program best suited for your needs and interests. The application deadlines for most admissions and financial aid decisions are from December to February for admission the next Fall, so the beginning of your Senior year is the time to begin planning for the application process.
There are generally four main factors in an application: your undergraduate transcript (GPA), Graduate Record Exam (GRE) scores, letters of recommendation, and a statement from you about your experience and your plans for your graduate career.
Your grades, of course, are the main record of your undergraduate achievements. Most quality graduate programs will require at least a 3.00 GPA or higher (on a 4 point scale). Fellowship programs will usually require a 3.50 GPA. Most programs will also emphasize your grades in physics classes and your grades in your Junior and Senior year over non-physics courses and courses taken in your early college career. So if you had a hard time getting adjusted to college and your Freshman year GPA is not so good, you can still be competitive if you had good grades in your upper division physics classes. Which courses you take are also important. (Your grade in Basket Weaving will not count very much.) Most programs will want to see at least one semester each of upper division Mechanics, Electricity and Magnetism, Quantum Mechanics, Statistical Mechanics, and an Advanced Laboratory.
Scores on the Graduate Record Exam (GRE) are also important for many programs. While your GPA depends on the institution that you attended and on which specific courses you have taken, the GRE is presumably an objective measure of your ability, both in general reasoning skills and in your specific physics knowledge. The general GRE has three parts: Verbal, Quantitative, and Analytical. While all parts are important, and indeed some programs just consider the total score, the second and third parts are generally considered more important for physics programs. The GRE is offered in a computer-based format, which can be taken by arrangement through the Educational Testing Service, who administers this test. The results of this test can take over a month to become available, so you should take it early enough in the Fall for the results to be available by the application deadline. More information on the GRE can be found at http://www.gre.org.
The final element in your application will be 3 letters of recommendation, usually from faculty members at your institution who are familiar with your work, and a statement of purpose indicating your plans for your graduate education. A letter of recommendation is generally more valuable if it comes from someone who has first hand experience with your work; for example, a faculty member that has supervised your Senior thesis or a summer research project. Letters from professors in your classes can be helpful, but a letter that only says “So-and-so got an A in my class” is generally less helpful. It is very advantageous to get to know some of your professors and work in their labs so they can get to know you personally. One or more strong letters of recommendation can overcome other weaknesses in your application, especially if the letter writer points out reasons for those weaknesses.
Your own statement of purpose is your chance to blow your own horn and highlight what you consider to be the main reasons a graduate program should be interested in you. If you have a specific area of physics that you are interested in, you should bring it up here. You should also point out any publications you may have co-authored as well as any other factors or experience that you have had.
Where should you apply to graduate school? Of course, there are many factors. The overall quality of the program is probably the most important to most students. The larger and more highly regarded programs will give you more options, and graduates of these programs have an advantage in the job market. If you have focused on a particular area of physics, you will want to consider programs that are strong in those areas. Condensed matter physics and high energy physics will be found at nearly all major institutions, although some are stronger than others or have different areas of emphasis. Other areas of physics, for example, atomic physics, biophysics, nuclear physics, plasma physics or space and atmospheric physics, are not always represented at every institution. You might have already established a relationship with a specific faculty member or program that could also influence your decision.
Personal factors can also be very important. Some students have a preference for the Midwest, the East or West Coasts, or the South. Some will prefer an urban setting, while others may prefer a small town or rural setting. Of course, the cost of living and other lifestyle issues may also be important: if you like cross-country skiing, don't move to Florida! Perhaps you want to stay close to (or move away from!) family and friends. The most challenging problem is if you are married or in a relationship where both of you have career goals. Finding an opportunity that can satisfy both partners can be difficult and require compromises. Sometime these factors seem to be less important than the physics-related issues, but if you're unhappy in your environment, it's likely you will not perform at your peak in graduate school.
In any case, there are a lot of things to think about when choosing to apply to a graduate school. One thing to keep in mind is that graduate school is, in some ways, much less structured than your undergraduate degree, and your success in graduate school is strongly dependent on your own motivation and hard work.
There are many good graduate schools in this country and abroad. Periodically the National Research Council publishes a rating, which gives an indication of overall quality. All of the schools in the top 30 provide excellent graduate educations in physics. Remember, though, that these ratings are already several years out of date by the time they are published.