Ch. 22 Section Summary - College Physics 2e _ OpenStax

22.1 Magnets

• Magnetism Overview

  • Concerns properties of magnets and their effects on moving charges.

  • Creation of magnetic fields through electric currents.

• Types of Magnetic Poles

  • North and south magnetic poles exist in pairs.

  • North magnetic poles are attracted toward Earth's geographic north pole.

  • Like poles repel; unlike poles attract.

22.2 Ferromagnets and Electromagnets

• Ferromagnetic Materials

  • Examples include iron, exhibiting strong magnetic effects.

  • Atoms in these materials act as small magnets (due to atomic currents).

  • Can align in domains; larger domains create permanent magnets.

  • The process of becoming magnetic is called magnetization.

  • Beyond Curie temperature: thermal agitation disrupts atomic alignment, and ferromagnetism vanishes.

• Electromagnets

  • Created using electric currents to generate magnetic fields.

  • Often enhanced by using ferromagnetic materials.

22.3 Magnetic Fields and Magnetic Field Lines

• Representation

  • Pictorially represented as magnetic field lines.

• Properties of Magnetic Field Lines

  • Direction is tangent to the field line.

  • Field strength is proportional to line density.

  • Field lines cannot intersect.

  • Always form closed loops.

22.4 Magnetic Field Strength: Force on a Moving Charge

• Formula:

  • Magnitude of force on charge q moving through a magnetic field is given by:F = qvB sin θ.

  • Where θ is the angle between charge direction and magnetic field.

• SI Unit:

  • Magnetic field strength is measured in tesla (T).

• Right Hand Rule 1 (RHR-1):

  • Thumb points in the direction of velocity, fingers in the direction of the magnetic field, palm perpendicular indicates force direction.

22.5 Force on a Moving Charge in a Magnetic Field: Examples and Applications

• Centripetal Force:

  • Magnetic force can act as centripetal force, causing circular motion.

  • Radius of the motion derived from component of velocity perpendicular to magnetic field.

22.6 The Hall Effect

• Definition:

  • Hall effect generates a voltage (Hall emf) across a current-carrying conductor in a magnetic field.

• Formula:

  • Hall emf provided by the width of the conductor and speed of charges moving through it.

22.7 Magnetic Force on a Current-Carrying Conductor

• Formula:

  • F = IlB sin θ,

  • I is the electric current, l is the length of the conductor, and B is the magnetic field strength.

• Right Hand Rule 1 (RHR-1) applies here as well.

22.8 Torque on a Current Loop: Motors and Meters

• Torque Formula:

  • Torque on a current-carrying loop in a magnetic field: τ = NIAB sin θ.

  • N = number of turns, I = current, A = area of the loop, B = magnetic field strength, θ = angle between the field and perpendicular to the loop.

22.9 Magnetic Fields Produced by Currents: Ampere’s Law

• Strength of Magnetic Field from a Wire:

  • Given by: B = (μ0I)/(2πr),where μ0 is the permeability of free space, I is the current, and r is the distance from the wire.

• Right Hand Rule 2 (RHR-2):

  • Thumb in current direction, fingers curl to show magnetic field direction.

• Magnetic Field in a Loop and Solenoid:

  • At center of loop: B = (μ0I)/(2R).

22.10 Magnetic Force between Two Parallel Conductors

• Force Formula Per Unit Length:

  • F/l = (μ0I1I2)/(2πr).

  • Attraction if currents go in the same direction, repulsion if in opposite directions.

22.11 More Applications of Magnetism

• Crossed Electric and Magnetic Fields:

  • Act as a velocity filter for charges with velocity perpendicular to the fields, governed by: v = E/B.