L8_Magnetic Field

Magnetic Fields Overview

Magnetism

  • Certain materials, known as magnets, attract tiny pieces of metal.

  • This attractive property is referred to as magnetism.

Magnetic Poles

  • Magnets have concentrated strength at their ends, termed the north and south poles.

  • The north-seeking end and south-seeking end are defined as N and S poles.

Magnetic Forces

  • Like poles repel each other while unlike poles attract.

Magnetic Field Lines

  • Magnetic field lines can be visualized by imagining a compass placed at various points.

  • The density of field lines indicates the strength of the magnetic field: dense lines indicate a strong field, sparse lines indicate a weak field.

Field Interaction Between Magnets

  • Lines between unlike poles demonstrate attraction while lines between like poles exhibit repulsion.

Magnetic Flux Density

  • Represented in webers per square meter (Wb/m²).

  • Magnetic field density is often referred to as flux density.

  • Flux lines are continuous and closed, indicating the direction of the B vector at any point.

Calculating Flux Density

  • Flux through area A can be calculated when the normal vector makes an angle with the B-field.

  • The relationship involves the cosine and sine of the angles.

Origin of Magnetic Fields

  • Magnetic fields are caused by charges in motion, rather than isolated magnetic poles.

Magnetic Force on Moving Charge

  • A charge moving in a perpendicular magnetic field experiences an upward magnetic force.

  • The force increases with higher charge, higher velocity, and a stronger magnetic field.

Direction of Magnetic Force

  • Use the right-hand rule to determine the direction of magnetic force:

    • Thumb: velocity (v)

    • Fingers: direction of the B-field

    • Palm: direction of force (F).

  • Force is maximized when the velocity is perpendicular to the magnetic field.

Definition of B-field

  • Magnetic Field Intensity (B) is defined as:

    • One tesla (T) produces a force of one newton (N) on a one coulomb (C) charge moving at 1 m/s perpendicular to the B-field.

Forces on Charges

  • Forces on negative charges oppose those on positive charges, requiring the left-hand rule for direction.

Indicating Direction of B-fields

  • Use crosses (X) for fields directed into the paper and dots (·) for fields directed out of the paper.

Practice Problems

  1. Identify the type of materials attracted by magnets.

  2. Determine where the strength of a magnet is greatest.

  3. Understand the effects of breaking a bar magnet.

Quiz Questions

  • Multiple choice questions assessing understanding on:

    • Properties and effects of magnetic fields.

    • Interaction of charges in a magnetic field.