Study guides › C/P › Physics
Electrostatics
Electrostatics describes the forces, fields, and energies of charges at rest. You will use Coulomb's law, draw and read field lines, separate potential from field, and predict how dipoles, conductors, and insulators behave.
Study this chapter in PrepMed (free)
What this chapter covers
- Charge & Coulomb's Law. Coulomb's law is the electric twin of gravity, and the MCAT loves its inverse-square scaling and its sign rules.
- Electric Field & Field Lines. The field turns the force between charges into a property of space, and field-line pictures are a favorite MCAT figure.
- Electric Potential & Potential Energy. Potential is the scalar that makes energy problems easy, but only if you keep it separate from the vector field.
- Dipoles, Conductors & Insulators. Water is a dipole and metal shields its interior; both ideas show up in biology and physics passages alike.
Key points to know
- Like charges repel, unlike attract; charge is conserved and quantized (e = 1.6×10⁻¹⁹ C)
- Coulomb force: F = kq₁q₂/r², so F ∝ 1/r²
- E = F/q; it points the way a positive test charge would be pushed
- Point charge: E = kQ/r², away from + and toward −
- V = kQ/r is a scalar; sum potentials with their signs
- ΔU = qΔV and W_by field = −qΔV
- Dipole moment p = qd points from − to +
- Uniform field: zero net force on a dipole, torque τ = pE sinθ
Try a practice question
What happens to the electrostatic force between two point charges if the distance between them is tripled?
- It decreases to one third
- It decreases to one ninth
- It increases nine-fold
- It increases three-fold
Show the answer
B. Force follows 1/r². Tripling r divides F by 3² = 9. A decrease to one third would describe a 1/r law, which is not Coulomb's law.
Common questions
What does this chapter cover?
Electrostatics covers Charge & Coulomb's Law, Electric Field & Field Lines, Electric Potential & Potential Energy, Dipoles, Conductors & Insulators.
What should I know first?
Like charges repel, unlike attract; charge is conserved and quantized (e = 1.6×10⁻¹⁹ C) Coulomb force: F = kq₁q₂/r², so F ∝ 1/r² E = F/q; it points the way a positive test charge would be pushed
21 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.