TEST TAKING TIPS

Write out basic formula
Look for easy answer
Sanity Check

numbers (v >> c?)
symbols (try 0, infinity)
units (F=ma...)

Sometimes part B can be answered without part A
Symmetry is your friend

Start by reading the question carefully, and determining what approach you should use. We have learned several ways to calculate the electric field or electric potential , it is a test of your knowledge to choose the right one. Can you use Gauss' Law (is there symmetry?). Does this require the principle of superposition? Is it a continuous or discrete charge distribution? What is dq? If the question is about capacitance, what is being held constant? The voltage? The charge?

Write out the basic formula: select the best formula from the formula sheet and write it down at the top of the problem- verbatim. Showing us the right approach is an important way to get partial credit. Do not just start by writing down numbers.

Look for an easy answer: we try not to make the test too long- it's not a test of endurance. Often, some part of a question has a very simple answer- for example: the electric field inside a conductor in electrostatic equilibrium is always zero.

Sanity check: this is very important! Does the number or answer make sense? If you get a velocity greater than the speed of light or a mass of a particle that is heavier than a sandwich, there is certainly something wrong. You can check an algebraic answer by letting r go to infinity or the separation approach zero and see if the change makes sense. Finally, in many cases you can plug in units and see if they work out. This is called dimensional analysis. In electromagnetism this can be tedious because many units are distantly removed from a force in Newtons or a time in seconds. It is admittedly a bit of an art, for example in a capacitance problem the check will go faster if you remember that epsilon-naught is also Farad/meter not just C²/N/m².

Sometimes part B can be answered without part A: We do not want you to get hung up on the first part of the problem, preventing you from showing us what you know on the rest of the problem. So sometimes we can write the problem so that you can completely answer a later part regardless of the first part. Look for this.

Symmetry is your friend: Symmetry is one of the most beautiful and profound tools of the physicist. You don't need to know the following for PY212, but there is a theorem that for every symmetry of nature there is a conservation law. On a more practical side, many problems are greatly simplified by the symmetry of the situation. Symmetry plays an especially important role in Gauss' Law (reread the chapter and look at your lecture notes if this is news to you!). But in other problems as well, ones that you have already solved in homework, a great simplification is generally present when, say, all the y-components of a force or field cancel. Learn to recognize when this happens as you solve homework and practice problems.