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17. Magnetic Forces

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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?

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» iTunes U (MP4 - 10MB)
» Internet Archive (MP4 - 10MB)

 

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?

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Download this video:
» iTunes U (MP4 - 14MB)
» Internet Archive (MP4 - 14MB)

 

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?

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» iTunes U (MP4 - 9MB)
» Internet Archive (MP4 - 9MB)

 

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?

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Download this video:
» iTunes U (MP4 - 9MB)
» Internet Archive (MP4 - 9MB)

 

Related Visualizations

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

 

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