Electrostatics
Electrostatics is the branch of physics that studies electric charges at rest — how they attract and repel through Coulomb's law, and the electric fields and potentials they create in the space around them.
Electrostatics deals with stationary electric charges and the forces, fields, and potentials they produce. Charge comes in two types, positive and negative; like charges repel and opposite charges attract. Charge is quantized in units of the elementary charge e (the magnitude of an electron's charge) and is conserved — it can move between objects, as when rubbing transfers electrons, but never created or destroyed.
The quantitative heart of the subject is Coulomb's law: the force between two point charges is F = kq₁q₂/r², proportional to the product of the charges and inversely proportional to the square of the distance between them. Doubling the separation cuts the force to one quarter — an inverse-square relationship exactly parallel to Newton's law of gravitation, except that electric forces can be attractive or repulsive.
Charges also alter the space around them. A charge creates an electric field E = F/q that points away from positive charges and toward negative ones, and moving a charge within that field involves electric potential energy and potential (voltage). Materials respond differently: conductors let charge flow freely and hold excess charge on their surfaces, while insulators pin charge in place. These ideas underlie phenomena from static cling to capacitors and set up the study of circuits.
The MCAT tests electrostatics in its Chemical and Physical Foundations section: expect Coulomb's law calculations, qualitative field and potential reasoning, and conceptual questions about charge conservation, conductors, and insulators — often woven into passages about electrochemistry, membranes, or laboratory instrumentation.
Key takeaways
- Electrostatics studies charges at rest; like charges repel and opposite charges attract.
- Coulomb's law gives the force between point charges: F = kq₁q₂/r², an inverse-square law.
- Electric charge is conserved and quantized in units of the elementary charge.
- Charges create electric fields and potentials; conductors move charge freely while insulators do not.
- The MCAT tests Coulomb's law math and conceptual field, potential, and conductor questions.