17. Magnetic Forces

• Course Home
• Syllabus
• Electric Fields

  • 1. Introduction to Electric Fields
  • 2. Math Review, Fields
  • 3. Electric Fields and Discrete Charge Distributions
  • 4. Electric Fields and Continuous Charge Distributions
  • 5. Gauss's Law
• Electric Potential

  • 6. Discrete and Continuous Distributions of Charge
  • 7. Equipotential Lines and Electric Fields
  • 8. Gauss's Law and Configuration Energy
• Capacitors

  • 9. Conductors and Insulators, Conductors as Shields
  • 10. Capacitance and Capacitors, Energy Stored in Capacitors
  • 11. Capacitors and Dielectrics
• Circuits

  • 12. Current, Current Density, Resistance, and Ohm's Law
  • 13. Batteries and Circuit Elements
  • 14. DC Circuits
  • 15. DC Circuits with Capacitors
• Magnetic Fields and Forces

  • 16. Magnetic Field
  • 17. Magnetic Forces
  • 18. Magnetic Dipoles
• Creating Magnetic Fields

  • 19. Biot-Savart Law
  • 20. Ampere's Law
• Faraday's Law

  • 21. Faraday's Law
  • 22. Inductance and Magnetic Energy
  • 23. RL Circuits
• Oscillating Circuits

  • 24. Undriven RLC Circuits
  • 25. Driven RLC Circuits
• Maxwell's Equations

  • 26. The Displacement Current and Maxwell's Equations
  • 27. Poynting Vector and Energy Flow in a Capacitor
• Electromagnetic Waves

  • 28. Maxwell's Equations and Electromagnetic Waves
  • 29. Energy and Momentum in Electromagnetic Waves
  • 30. Generating EM Waves, Dipole Radiation and Polarization
• Nature of Light

  • 31. Interference
  • 32. Diffraction
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Learning Objectives

• To be able to describe the motion of a charge in a uniform magnetic field.
• To comprehend how a velocity selector works.

Preparation

Course Notes

Read through the course notes before watching the video.  The course note files may also contain links to associated animations or interactive simulations. 

The Magnetic Field (PDF)

Lecture Video

Video Excerpts

Learning Activities

Guided Activities

Read through the class slides. They explain all of the concepts from the module.

Slides (PDF)

Self-Assessment

Do the Concept Questions first to make sure you understand the main concepts from this module. Then, when you are ready, try the Challenge Problems.

Concept Questions

Concept Questions (PDF)

Solutions (PDF)

Challenge Problems

Challenge Problems (PDF)

Solutions (PDF)

Problem Solving Help

Watch the Problem Solving Help videos for insights on how to approach and solve problems related to the concepts in this module.

Problem 1: Electron Gyrating in a Magnetic Field

An electron moves in a clock-wise direction in a semi-circle in a magnetic field. What is the direction and magnitude of the magnetic field that causes this motion? What is the time it takes for the electron to traverse the semi-circular path?

Problem 2: Mass of an Isotope

An isotope of aluminum which is singly charged moves in the crossed electric and magnetic fields of the velocity selector of a mass spectrometer. The magnitude of the electric field is E and of the magnetic field B. What is the velocity that is selected by this arrangement? The ion then moves into a region with a magnetic field of the same magnitude, and with no electric field, and subsequently moves in a circle of radius R meters. What is the mass of this aluminum ion in terms of the quantities given?

Problem 3: Force on a Wire in a Magnetic Field

A current carrying wire of length l carries current in the y-direction. It is immersed in a constant magnetic field B with a given orientation. What is the force per unit length on the wire? What is the total force on the wire?

Problem 4: Magnetic Interaction of a Wire and a Rectangular Loop

A long straight wire carries a current I₁. There is a rectangular loop with its long sides parallel to the wire, which carries a current I₂. The long sides of the loop and the wire all lie in the same plane. The nearer side of the rectangular loop is a distance r₁ away from the wire, and the more distance side is a distance r₂ from the wire. What is the force that the rectangular loop feels as a result of the current in the wire?

Related Visualizations

The visualizations linked below are related to the concepts covered in this module.

• The Dip Needle
• The Earth and a Giant Dip Needle (Far)
• Charge Moving in a Magnetic Field (Front)

 

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