Due to many-many-many (about 2) requests from my friends and faculty mates, finally, I’m writing this post now, as the dates of the GRE subject tests are getting closer and closer (first quarter of April).
As my specialization is physics and I’m applying to the graduate schools in the US, I was required to pass the GRE physics test. Due to idiocy of the Armenian government, I’m only allowed to enter top 10 universities of the world. So I really wanted to get as much as I can, in order to have at least any chance to enter.
This post contains mainly my personal experience, advices and several useful links, as the more official information can be found by googling.
First of all, several things you really need to know.
Scoring system
The top score you can get in this test is 990. As it is written in forums and unofficial guides, nobody knows why 990 not 1000, even ETS doesn’t. In this test you have 100 questions and 2 hours 50 minutes for that. If you think it’s too much, well… it’s actually not. That’s approximately 102 seconds for each question. GRE physics is a test, which means you have 5 options for each question. Actually, grading system is simple: you’re answering correct, you get $$+1$$ to the raw score, wrong $$-1/4$$ to the raw score. If you do not answer the question, you’re not charged. So unlike other tests, in GRE physics it sometimes makes sense not to answer the question at all. Then the raw score (from 0 to 100) is being converted to the actual test score (from 200 to 990). The way they do this conversion is a mystery. The conversion system changes every year, fitting the results of test takers and the difficulty of the test itself.
The fact is, that you can get 990, even if your raw score is less than 100. As for me, I didn’t answer to about 3-4 questions, but I still got my 990.
What kind of physics you should know
The questions are mostly from the university level physics, however some of them may seem pretty easy for high school students. Not talking about the basic knowledge of classical mechanics, electromagnetism and quantum mechanics, you’ll sometimes need to know the titles of some rarely used effects and phenomena, like “Bragg-Wolf formula” etc. I’ll discuss more details for each section further. But what I want to advice to those who’re starting to study for the April test just now, I’m pretty sure that blindly reading long books in physics theory is not a good idea. You see, you should have already got all the theory during your undergraduate studies (3 years, or whatever). Now it’d be better to focus on gaining more skills on test itself, on strategy, problem solving etc.
Advices for each section
1. Mechanics + special relativity
Well, it would seem strange, but the most difficult section that everyone makes a lot of mistakes appear to be the classical mechanics. The reason is, they’re usually more tricky and demand more time to solve. ETS test makers are smart enough to put two answers, besides the correct one, that you’re likely to obtain by solving the question not quite right. For example, if you do not take into account some friction force, or wrote the equilibrium condition wrongly, or you do not remember whether there is a plus or minus sign against the potential energy in gravitational field, you’re likely to get caught on this section. This tricky parts are something to be concerned about, so if you have this sort of question - you better recheck your solution and answer.
In special relativity you’re required to have at least any idea about how things are going on higher velocities. Like drawing plots in $$(t,x)$$ terms would be a good idea. The important thing here is to remember the one-dimensional Lorentz-boost (better in terms of $$\gamma$$ and $$\beta$$), the formulas for the relativistic energy and momentum (also in terms of $$\gamma$$ and $$\beta$$).
2. Electromagnetism
The most difficult part in this section is to visually understand what kind of fields are made, say, by a round wire with a constant current, or a straight wire, or a cylinder etc.! The configuration of these fields and the formulas will also be very useful. It’s easier to memorize the formula for, i.e., a round wire, than to derive it again and again from Bio-Savara law. The directions of the Lorentz’s and Ampere’s forces and the interaction of wires with currents will also be useful to memorize. So you have a lot of work to do.
Finally, I strongly advice to memorize correctly Maxwell’s equations in differential and integral form, and, of course, remember their physical meaning, as there appear plenty of questions on them.
You also need to know the physics of circuits and electrostatic conductors (probably with dielectric material inside). The questions on circuits are not too difficult, but, you know, you better get used to them to feel confident.
3. Quantum things + atomic physics
You must learn to work with $$\mid \text{bra}\rangle$$ and $$\langle \text{ket}\mid$$ notations and of course, you sould know their physical meanings. The basic knowledge in quantum mechanics is pretty enough.
In case of atomic physics, as for me, the most important things are the numerical calculations and SI to CGS conversions. Simple advice from me is to memorize the constants or combinations of constants like $$hc = 12400~\text{eV}\r{A}$$, in a correct system of measurement. Again, you’ll quickly get what you need if you do more and more practice tests.
Important material
First of all, the practice tests and sorted questions can be found here. As there are not too many of these tests, I advice to do about 1 per two weeks, studying on your own weaknesses during the pause. The link here contains full solutions to each of the question from these tests, in case if you need.
Here and here you can find some important formulas on each section as well as tips and tricks, like here.
And finally, here are some theory on QM and atomic physics and the so-called specialized topics.
Strategy and time management
As I said before, 102 seconds is not much for each question, as some questions may require a lot more time, some - probably less. If you feel that the question is complicated, you can’t find the solution, or the answer you get does not meet any of the five given options, just skip it! Mark the number somewhere and skip it. They usually put difficult questions at first, so that you spend a lot of time for them and not have enough time for other easy ones, so keep it in mind.
You’re NOT allowed to use calculators, so try to practice without it and find some ways, develop some personal methods of doing quick calculations, working with powers of ten etc.
When you’re finished and still have time, you may turn to the questions that you skipped, but don’t guess! You have only a chance of $$1/5$$ to get a correct answer, so you’re not likely to be lucky. Remember, wrong answer subtracts $$1/4$$ from the raw score, so be careful. Sometimes, of course, excluding some wrong answers out of 5 may help you to guess. But again, if you don’t have any idea about the matter of the question, don’t guess!
While practicing, do not just solve problems. Try to bring your test-taking abilities to mechanical behavior, memorize as much as you can, it will really help you to save a lot of time.
And always remember, that this test, as any other ETS test, checks your ability to pass this test. Good luck!
cd ~