MCAT Physics > Electrostatics
Charge (C) can be either positive (proton) or negative (electron).
Elementary Charge (q) = 1.6 x 1019 C
Coulomb's Law represents the magnitude of the electrostatic force on two charges
F = k(q1q2)/r2 = Eq
- Coulomb's Constant (k) = 9.0 x 109 = (πε0)/4
- ε0 = 9.0 x 10-12
This equation relates to the organic chemistry section of the MCAT. For example, in chemical bonding, more specifically ionic bonding there is negative electrostatic energy because q1 and q2 are opposite in charge and therefore attract. If they were positive in charge then the molecules would repel each other and no bonding would occur.
- Opposite charges attract (negative F value)
- Positive charges repel (positive F value)
The greater the magnitude of electrostatic potential, the stronger the ionic bond will be. Strong ionic bonds are most commonly found by looking for a high electrostatic charge (q) that are very close together (r). Compounds and molecules that form strong ionic bonds have high charge density (charge:size).
A common theme to note when figuring out problems related to Coulomb's law is to realize that larger magnitude charges that are closer together will result in a higher electrostatic force. To understand this trend will help you answer questions on the MCAT quicker as you can quickly rule out wrong answers.
Another trend to notice on the MCAT is when q1 doubles, then so does the electrostatic force. This is a direct relationship. If the radius (r) halves than the electrostatic force increases by an exponential amount. So for example, if the radius was 2 and it is reduced to 1, then the electrostatic force will double to 4. If the radius was 3, then the electrostatic force would become 8.
22 = 4
23 = 8
On the MCAT the negative sign is often not used and an absolute electrostatic energy value is used instead. Be careful of this when answering questions.
Coulomb's law is analogous to Newtons Law of Gravitation, which represents gravitational forces instead of electrostatic ones. This can be seen in the forces and mechanics section of About the MCAT. The only difference between gravitational force and electrostatic force is that the electrostatic force is a much stronger force.