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Electrostatics and Magnetism

Chapter 5: Electrostatics and Magnetism

Updated Mar 26, 2026
Read the entire chapter on one page Every section in order, with the sidebar tracking where you are as you scroll.
🎯 Diagnostic: Test Your Starting Level 24 questions (2 per section). No prior reading required, see what you already know.

Aim to answer every question before checking. Missed questions point you to the sections you need most.

1. (5.1) Electric charge is:
A. Total charge is conserved in an isolated system.
2. (5.1) Like charges:
B. Electrostatic force is along the line connecting the charges.
3. (5.2) Coulomb's law is:
C. Same inverse-square structure as gravity but much stronger per unit mass/charge for everyday objects.
4. (5.2) The Coulomb constant k has value:
D. Related to the permittivity of free space via k = 1/(4πε₀).
5. (5.3) The electric field E at a point is:
A. Gives force on any charge placed at the point via F = qE.
6. (5.3) Electric field lines:
B. Two crossing lines would mean two different field directions at one point, which is impossible.
7. (5.4) At distance r from a point charge Q, the electric field has magnitude:
C. Inverse-square falloff, consistent with Coulomb's law.
8. (5.4) Between parallel plates (one +, one -):
D. This uniform field is what makes parallel-plate capacitors so useful.
9. (5.5) Electric potential energy between two point charges:
A. Falls off as 1/r (unlike force, which falls as 1/r²).
10. (5.5) The work done by the electric field on a charge q moving from A to B is:
B. Positive charges "fall" toward lower potential; negative charges the opposite.
11. (5.6) Electric potential V is:
C. A scalar field, easier to work with than E (vector) in many problems.
12. (5.6) At distance r from a point charge Q:
D. V falls off as 1/r; E falls off as 1/r².
13. (5.7) Equipotential surfaces:
A. Like contour lines on a topographic map, but for potential.
14. (5.8) An electric dipole consists of:
B. Many molecules (e.g., water) have permanent electric dipoles.
15. (5.9) A magnetic field is produced by:
D. In special relativity, magnetism is a consequence of motion relative to charges.
16. (5.9) The SI unit of magnetic field B is:
D. Earth's field is ~50 μT; fridge magnets ~10 mT; MRI machines 1-3 T.
17. (5.10) The magnetic force on a moving charge is:
A. Magnetic force curves the trajectory of a moving charge into a circle but cannot change its speed.
18. (5.10) A positive charge moving east in a magnetic field pointing straight up experiences force:
B. Point fingers east, curl up → thumb points south (for positive q).
19. (5.11) The magnetic force on a straight current-carrying wire of length L in a uniform B is:
C. Underlying principle of motors: current through a coil in a B field creates a torque.
20. (5.11) Two parallel wires carrying current in the same direction:
D. Opposite-direction parallel wires repel. The definition of the ampere was based on this force between wires.
21. (5.12) Faraday's law of electromagnetic induction:
A. Underlies generators, transformers, and induction cooktops.
22. (5.12) Lenz's law says:
B. The minus sign in Faraday's law encodes Lenz's law. It ensures energy conservation.
23. (5.2) The Coulomb force between two 1 C charges 1 m apart is:
C. 1 coulomb is a huge charge; normal electrostatics problems use µC or smaller.
24. (5.8) The electric field inside a perfect conductor at electrostatic equilibrium is:
D. Basis of Faraday cages, which shield their interior from external fields.

You pull a sweater over your head on a dry winter day and your hair stands straight up. You shuffle across a carpet in socks and get zapped when you touch a doorknob. These are not random annoyances - they are electrostatics in action. The same invisible force that makes your hair defy gravity also holds electrons in orbit, drives nerve impulses, and powers every electronic device you have ever used.

Electrostatics and magnetism might sound like two separate topics, but they are deeply intertwined. A moving electric charge creates a magnetic field. A changing magnetic field creates an electric force. This connection - electromagnetism - is one of the four fundamental forces in the universe and one of the most heavily tested physics topics on the MCAT. If you master the handful of equations in this chapter and understand the conceptual reasoning behind them, you will be equipped to handle virtually any electromagnetism passage on test day.

The MCAT focuses on a specific, manageable slice of this enormous field: Coulomb’s law, electric fields, potential energy vs. voltage, dipoles, magnetic force on charges and wires, and Faraday’s law at a conceptual level. No calculus required. Every formula you need fits on a single index card. The challenge is not the math - it is keeping the concepts straight. That is exactly what this chapter is designed to help you do.

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