The Sciences

An Inside Look at the Physics GRE

By John ConwayOct 22, 2009 12:01 PM


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I am just back from Princeton where we held the annual meeting of the GRE Physics Committee of Examiners, a group of six, ahem, distinguished professors (we have grey hair) who sit around a conference table working through hundreds of potential and actual Physics GRE problem. Each year new exam forms are completed, new questions added to the pool, statistics reviewed, and a good time is generally had by all.

This was my last meeting - I have served on the committee for six years. The membership rotates roughly every two years. I had been an external reviewer and problem writer for a couple years, and was then asked to serve on the committee. I am sworn to secrecy about a lot of the details, for good reason, but let me try to tell you from my perspective as an exam writer how to study for this dreaded event in your physics education.

Firstly, there's the format. The exam is 100 questions long, and you have 170 minutes to do it. This is, therefore, different from just about every other physics exam you have had in college, where you have, say, four to six problems in an hour-long exam. The GRE Physics problems (or "items" in assessment world jargon) are short, to-the-point questions, and just about all of them are short calculations, if any, and take little time once you see what to do. Writing such questions is a difficult thing to do, let me tell you. We are continually amazed how, after about six levels of review, we can find issues of clarity, reasoning, and even sometimes basic physics correctness in the items submitted to the pool. All the committee members spend a lot of time each year reviewing hundreds of problems, looking for flaws, but more often than you would think the face-to-face meeting in Princeton with the ETS folks reveals something previously overlooked. It's a really interesting process.

For each new exam form we eventually arrive at 100 items that test mastery of a clear physics concept or idea, and there is, yes, a certain amount of memorization required in terms of the basic equations learned in undergraduate physics. But there are many problems that can be done using just concepts, and many that can be done with simple dimensional analysis. When there are numerical solutions (and many if not most are in that category) the numbers are chosen so as to allow easy arithmetic - no calculators are allowed.

My first piece of advice to students studying for this exam is to focus on reviewing the textbook from your freshman introductory physics course. In my years on the GRE committee, when I have needed to consult a text, it is that text at least 80% of the time. If you master every example in there and review the basic equations, you will do really well on the GRE. I have found that only a small fraction of the items on the GRE are actually from upper-level topics like stat mech, quantum, and special topics (solid state, nuclear, particle, cosmology, etc.) And presumably you have been studying the advanced topics more recently anyway. I think the single biggest mistake students make in studying for the GRE is to focus on too-advanced subjects.

The other piece of advice I give students is to be disciplined in your approach to actually taking the exam. You only have an average of 1.7 minutes per problem! If you get bogged down on a long algebraic calculation, you risk not being able to complete the exam, including items that you would correctly answer in a few seconds. So when you take the exam, read each problem, answer it if you can do so reasonably quickly and then put an X on the problem number. If you think the problem will take some time or a long calculation, put a circle around the number and come back to it in a second pass through the whole thing. But pIck off the easy ones first! It also helps build confidence as you go through.

Also realize that the GRE penalizes random guessing: your raw score is the number correct minus the 1/4 times the number incorrect. As a result it's no better to guess than to leave an answer blank if you cannot eliminate some of the five choices. But if you can eliminate some, then by all means guess! Look carefully at the possible answers - sometimes just the units, or magnitude, or mathematical form can give you a way to guess more astutely.

So just what is the GRE measuring? A critic might point out that it measures the ability to work under pressure, memorization, and quick mathematical reasoning and calculation. Though these are good qualities for a physicist to have, they are by no means the only qualities required for a successful career. I would argue further, though, that the Physics GRE really does test knowledge about basic physics and the ability to analyze physical situations accurately.

So then how important is the Physics GRE for your career? It turns out that it is in fact quite important. Some of the top programs in the US even go to the extent of requiring a GRE score above some threshold for considering the applicant. I have served on our graduate admissions committee for five years now, and I can tell you that we regard the GRE as just one piece of information telling us how likely a student is to thrive in our program. We do see a clear correlation between an incoming graduate student's Physics GRE score and their score on the other dreaded exam in a physics student's career, the Ph.D. written preliminary exam, which is a very different beast. (There was, a few years back, some lore that the GRE Verbal score was a better predictor than the GRE Physics score, and there is a correlation, but not as strong as with the GRE Physics score.)

In considering an applicant we look at a number of things, including the applicant's own statement, experience, letters of recommendation, and their undergraduate transcript, in addition to the GRE general and subject scores, to get an idea of the whole student. My own observation is that students below about the 30% level have a very hard time attaining a Ph.D., though this is by no means absolute. I am sure there are tons of very successful physicists out there who, for whatever reason, scored poorly on this peculiar exam and went on to great careers.

So, to of those of you facing this exam in a few weeks, I wish you good luck! Review your intro course, get a good night's sleep before the exam, and make sure you pick off all the easy problems that you can!

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