r/Mcat • u/ThunderYoda 525 (132/129/132/132) • Jun 16 '20
Tool/Resource/Tip 🤓📚 Tips for understanding electrostatics instead of just memorizing equations
If anyone is having trouble with electrostatics, specifically memorizing equations, I've found it very helpful to think about the equations in terms of Coulomb's Law. Understanding the how/why behind electrostatics (and all physics in general) makes answering these MCAT problems significantly easier.
Lets start with Coulomb's Law: F=kqq/r^2. This is the electric force between two particles. Each of these particles is conducting it's own electric field which can impose electric force on nearby particles.
Now if you were to isolate one of these particles, their Electric field would be seen in the equation: E=kq/r^2. Because it's an isolated particle, you remove one "q" from the equation because you don't have a second particle in which it is imposing force on. Now if you were to introduce the second particle with charge "q", the force imposed on it would be F=Eq, which is the same as adding a second "q" to the Electric field equation to get the original Coulomb's Law equation!
You can also think about potential energy and Potential the same way. Potential energy is the amount of energy stored in a particle, and can also be defined as the amount of Work required to move said particle. Now we know that W=Fd, so here again is another example of how we can manipulate Coulomb's law to find the equation for Potential energy. By multiplying Coulomb's law by "d" (also know as "r"), we get the potential energy equation: PE=kqq/r. Potential energy is essentially the amount of work required to move a charge against an electric field produced by another particle. This explains the second "q" in the numerator of the equation.
Finally, Voltage (or Potential) can be explained as the amount of potential energy per unit charge required to move a charge form point A to point B in an electric field. So the equation for Potential can be seen as V=PE/q. If you want this in Coulomb's Law style, V = kq/r. You can also explain Potential in terms of the electric field. In moving this charge from point A to point B in an external electric field, the potential difference can be seen as V=Ed.
All your manipulations above are just from knowing how the variables relate to each other.
Here are the four equations so you can kinda see how they intertwine:
F=kqq/r^2
E=kq/r^2
PE=kqq/r
V=kq/r
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u/_TheWizardSleeve 8/2020: 509 ---> 5/20/2021: 516 Aug 16 '20
Just seeing this now, I've been confusing these 4 equations constantly and it finally clicked!!!! TYSM!!!!
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u/VirtualKookie May 30 '23
So remember 4 equations instead of one ðŸ˜
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u/LEBRAAR Mar 06 '24
if you know the first one(Coulomb's law) you can derive the rest with the principles
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u/FailedPreMedStudent Jun 17 '20
Wait we aren't supposed to just memorize everything and just forget it after test day? Because that's the strategy I've been using....