Physics · MU Sofia

16. Magnetic field Magnetic field of a permanent magnet.

Covers field lines running from north to south pole, the magnetic force on a moving charge and how it depends on velocity and angle, and circular motion in a uniform field. It then introduces the Lorentz force formula, a mass spectrometer, solenoids, Ampere's law and the fields of circular conductors and solenoids, ending with charge motion in combined fields. Several diagrams support the text.

Inside: 2 sections · 7 labelled pictures · 10 flashcards · 3 min

Topic 17 of 42 in the MU Sofia syllabus for Physics (Medicine, Year 1). The free AceMed note covers it in 2 sections, about 504 words (3 min of reading), with 10 flashcards.

In this note

  1. Introduction
  2. Lorentz Force Formula F= q(E+v*B)

Introduction

Summary

  • Magnetic fields, whether from permanent magnets or electromagnets, are delineated by field lines extending from the north to the south pole. Charged particles' behavior in these fields depends on their velocity and the angle of approach, affecting the magnetic force they experience. This concept is crucial in applications like mass spectrometers for ion separation based on mass-to-charge ratios and solenoids that generate magnetic fields with electric current. Ampere's Law connects the magnetic field in a loop to the current passing through it, integral for understanding magnetic fields around conductors. The Lorentz force equation, indicating the combined electric and magnetic forces on charged particles, further elucidates the interaction between charged particles and these fields.

Magnetic Field of a Permanent Magnet

  • Field Lines: Stretch from the north to the south pole.
  • Particle Motion: No magnetic force (Fb = 0) when a particle moves parallel or antiparallel to the magnetic field. The magnetic force (Fb = qvB\sin\theta\) depends on the charge (q), velocity (v), magnetic field (B), and angle (theta) between (v) and (B).
  • Motion in Uniform Magnetic Field:
  • The force (F) on a charged particle equals (m)(a.c) (centripetal acceleration).
  • The period of motion (T), or time for one revolution, is

What Is Lorentz Force?

  • Lorentz force is defined as the combination of the magnetic and electric force on a point charge due to electromagnetic fields. It is used in electromagnetism and is also known as electromagnetic force. In the year 1895, Hendrik Lorentz derived the modern formula of Lorentz force.

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