Mastering the SAT Subject Tests, Easier Than You Think! – Physics

Posted by Alex O. on 9/17/18 11:08 PM

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Take math and apply it to real-world phenomena, and one of the things you get is physics! The Physics SAT Subject Test is a great way to show universities that you have a solid understanding of using math concepts to approach complex problems. As a result, taking the Physics Subject Test can be beneficial not only for those hoping to pursue science and engineering but also those thinking about business, economics, and political science. So let’s talk about the Physics Subject Test!

What is the Physics SAT Subject Test?

The Physics Subject Test is a 1-hour, 75-question exam testing your knowledge from an expected one year of high school physics. The test covers four areas (listed from most covered to least covered on the test): mechanics, electricity and magnetism (E&M), waves and optics, and heat and thermodynamics. 

What should I study?

The College Board website lists what specific topics are covered in each of the four areas. You must be familiar with all of the topics and be able to identify them in a question. For example, if a figure has a line with a small break in the center (a slit) and the question asks about shining a light in different areas, you can bet the question is going to be testing your understanding of single-slit diffraction. The nice thing about this subject test is that with enough practice, you should be familiar with almost all questions that will be asked on the test. It’s really hard to come up with completely unique questions in high school physics. So practice tests are your best resource!

What about tips for the test?

While being familiar with all the topics is essential, here are several tips to help you figure out what a question is asking and how to answer it correctly.

  • Remember the difference between a scalar and a vector. In mechanics, for example, this can be the difference between energy (a scalar) and momentum (a vector). If a ball of mass m moving to the right at a velocity with magnitude v hits a wall and then bounces back to the left with a velocity still with magnitude v, what happens? Well, since

Energy = (1/2)*m*|v|^2

then the energy did not change. Its change is 0. But momentum is a vector, where

Momentum = m*v

so momentum changed by -2*m*v, since it completely reversed direction.

  • Minimize the amount of math you’re doing. Remember this is a physics test, not a math test. Consider a circuit where a voltage source is put in series with a resistor. We know

Power dissipated originally = V^2 / R

If we double the voltage, how does the power dissipated change? First, minimize how many variables you use. So your new voltage is 2V, where V is the original voltage, and

Power dissipated now = (2V)^2 / R

Then, pull out the numbers and find how the new equation relates to the old one

Power dissipated now = 2^2 * V^2 / R = 2^2 * (Power dissipated originally)

We can see that the power has increased by 4 times the original amount. We didn’t need to put in any numbers except for “2.”

  • Let units help you if you’re uncertain. Don’t remember what specific heat is? Look at the units on the answer choices. They will likely all have “J/kg/°” If the question gives you information in units of J, kg, and °C, then the problem might be as simple as plugging those numbers into the fraction. However, you shouldn’t fully rely on this as sometimes physics isn’t that simple. Use this as a last resort if you have no idea how to approach a problem.
  • Pay attention for keywords. “Frictionless” is one example, which usually denotes the absence of an extra force (to simplify the problem) or to say that no energy is dissipated by heat/friction (when using conservation of energy to solve a problem). Other keywords include vector, time, and constant.
  • Remember formulas and patterns. Remembering the formula for the period of a small-angle pendulum or remembering the formula for the gravitational force are basically essential since there is no timely way of deriving them on the test. Also, remember graphical relationships between different characteristics. For example, if acceleration is constant (flat) over time, velocity is a line with a slope, and position is a parabola over time.
  • But don’t be afraid to double check with common sense. A question may say, “A satellite is orbiting the Earth. If the distance from the satellite to the center of the Earth is halved, what happens to its speed?” Think about where you have seen something like this before. A common example is an ice skater spinning in circles with her arms out. If she pulls her arms (the satellite) inwards, she’ll start to spin much more quickly. Without going through the formulas, you then know the satellite should speed up if pulled in closer to the Earth.

As always, the best preparation is lots and lots of practice tests. While you’re taking these tests, make sure to apply these tips so you can more efficiently approach problems. Stay tuned for the next few posts in my blog series where I’ll switch from math and science to talking about improving scores on language subject tests!

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