The Lorentz force is the total electromagnetic force on a charged particle, F = qE + qv×B. Its magnetic part (qvB sinθ) acts perpendicular to both the particle's velocity and the magnetic field, so it changes the particle's direction but never its speed.
The Lorentz force is the full electromagnetic force on a charged particle, combining the electric force qE and the magnetic force qv×B. On AP Physics 2, the magnetic piece gets most of the attention. Its magnitude is F = qvB sinθ, where θ is the angle between the velocity and the magnetic field, and its direction comes from the right-hand rule (point fingers along v, curl toward B, thumb gives F for a positive charge; flip it for a negative charge).
Here's the part that makes the magnetic force weird and useful. Because it's always perpendicular to the velocity, it does zero work on the particle. It can't speed the particle up or slow it down. All it can do is bend the path. That's why a charge moving perpendicular to a uniform magnetic field travels in a circle, with qvB acting as the centripetal force. Set qvB = mv²/r and you can solve for the radius, which is the math behind mass spectrometers and velocity selectors.
The Lorentz force lives in the magnetism and electromagnetic induction unit of AP Physics 2, where you're expected to predict both the magnitude and direction of forces on moving charges and current-carrying wires. It's the bridge concept of the whole unit. The force on a wire (F = BIL sinθ) is just the Lorentz force on many charges at once, and motional EMF exists because the magnetic force pushes charges along a moving conductor. It also pairs naturally with mechanics, since AP loves asking you to combine qvB with circular motion (centripetal force) or with energy reasoning (the magnetic force does no work, so kinetic energy stays constant). If you can't use the right-hand rule fluently, this entire unit gets hard fast.
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Magnetic Field (Unit 12)
The magnetic field is what exerts the Lorentz force in the first place. A field of strength B pushes on a charge q moving at speed v with force qvB sinθ, so every magnetic force problem starts by identifying B's direction (often drawn as dots out of the page or X's into the page).
Right Hand Rule (Unit 12)
The right-hand rule is how you find the Lorentz force's direction. Fingers point along velocity, curl toward the field, thumb gives the force on a positive charge. For electrons, do the rule and then reverse the answer. Roughly a third of magnetism MCQs are really just right-hand-rule checks.
Electric Field and Coulomb's Law (Unit 10)
The qE term of the Lorentz force comes straight from Unit 10. A velocity selector is the classic crossover problem, where the electric force qE and the magnetic force qvB point in opposite directions and only particles with v = E/B pass straight through.
Electromotive Force (EMF) (Unit 12)
Motional EMF is the Lorentz force in disguise. When a conducting bar moves through a magnetic field, the magnetic force qvB pushes free charges to one end of the bar, building a potential difference. That's the microscopic reason a moving rod acts like a battery.
No released FRQ uses the phrase "Lorentz force" verbatim, since College Board usually says "magnetic force on a charged particle," but the physics shows up constantly. Multiple-choice stems give you a charge moving through a field region and ask for the force direction (right-hand rule), the radius of circular motion (set qvB = mv²/r), or what happens to kinetic energy (nothing, because the force does no work). FRQs build the same ideas into mass spectrometers, velocity selectors, and rails-and-rod induction setups, and they often ask you to justify in words why the path is circular or why the speed stays constant. Practice writing that justification cleanly, because "the force is perpendicular to velocity, so it changes direction but does no work" is exactly the sentence graders want.
The electric force acts on any charge, moving or not, and points along the field line (with the field for positive charges, against it for negative). The magnetic part of the Lorentz force only acts on moving charges, points perpendicular to both v and B, and does no work. The electric force can change a particle's speed; the magnetic force can only change its direction. The full Lorentz force F = qE + qv×B includes both.
The Lorentz force is the total electromagnetic force on a charge, F = qE + qv×B, and the magnetic part has magnitude qvB sinθ.
The magnetic force is always perpendicular to the velocity, so it does zero work and never changes the particle's speed or kinetic energy.
A charge moving perpendicular to a uniform magnetic field travels in a circle, and setting qvB = mv²/r lets you solve for the radius.
Use the right-hand rule for the force direction on a positive charge, and reverse the result for a negative charge like an electron.
A stationary charge feels no magnetic force at all, and a charge moving parallel to the field feels none either since sinθ = 0.
The force on a current-carrying wire (F = BIL sinθ) and motional EMF are both the Lorentz force applied to many moving charges at once.
It's the total electromagnetic force on a charged particle, F = qE + qv×B. On the AP exam, the magnetic part matters most. It has magnitude qvB sinθ and points perpendicular to both the velocity and the magnetic field, with direction given by the right-hand rule.
No, never. Because the force is always perpendicular to the velocity, it can't transfer energy. The particle's speed and kinetic energy stay constant; only the direction of motion changes. This is a favorite conceptual MCQ trap.
The Coulomb (electric) force qE acts on any charge, even one at rest, and points along the field. The magnetic force qvB only acts on moving charges and points perpendicular to both v and B. A velocity selector problem uses both at once, balancing them so v = E/B.
When velocity is perpendicular to a uniform field, the force qvB stays perpendicular to the motion at every instant, which is exactly the condition for uniform circular motion. Setting qvB = mv²/r gives the radius r = mv/(qB), the equation behind mass spectrometer problems.
There's no magnetic force, since qvB = 0 when v = 0. A stationary charge can still feel an electric force qE if an electric field is present, which is the other half of the full Lorentz force equation.