Chapter 27: Magnetic Field and Magnetic Forces

Students learn how magnetic fields arise from moving charges and create vector fields measured in tesla units, with field lines that form closed loops from north to south poles. The magnetic force on a moving charge follows the cross product relationship F = q × v × B, always acting perpendicular to both velocity and field direction, causing charged particles to follow circular or helical trajectories without changing their kinetic energy. The chapter explores practical applications including velocity selectors that use crossed electric and magnetic fields to filter particles with specific speeds, and mass spectrometers that separate ions based on their mass-to-charge ratios through controlled circular motion in magnetic fields. Current-carrying conductors experience magnetic forces described by F = I × l × B, forming the operational basis for speakers and motors, while current loops develop magnetic dipole moments that experience torque when placed in external magnetic fields. Direct current motors convert electrical energy to mechanical work through magnetic torque on rotating coils, utilizing commutators to maintain continuous rotation against back electromotive force. The Hall effect demonstrates how magnetic fields deflect charge carriers in conductors, creating measurable transverse voltages that reveal charge carrier properties and enable precise measurements of magnetic field strength, carrier density, and drift velocity in materials.