# Magnetic Forces and Fields

Student Learning Objectives
Lessons / Lecture Notes
Important Equations
Example Problems
Applets and Animations

Student Learning Objectives

• To acquire familiarity with basic magnetic phenomena.
• To understand the force that a magnetic field exerts on a moving charge.
• To study the motion of charged particles in magnetic fields.
• To understand the magnetic forces and torques on wires and current loops.
• To study the magnetic fields due to currents in wires, loops, and solenoids.

Lessons / Lecture Notes

PY106 Notes from Boston University (algebra-based):

Introductory physics notes from University of Winnipeg (algebra-based):

HyperPhysics (calculus-based)

PHY2049 notes from Florida Atlantic University (calculus-based):

PHY2044 notes from Florida Atlantic University (calculus-based)

General Physics II notes from ETSU (calculus-based)

Important Equations

Example Problems

Problem 1
A particle of charge +7.5 μC and a speed of 32.5 m/s enters a uniform magnetic field whose magnitude is 0.50 T. For each of the cases in the figure below, find the magnitude and direction of the magnetic force on the particle. (Solutions)

Problem 2
A long straight wire carries a 15.0 A current to the left. At a particular instant, a point charge q = +5.0 μC moving at 1.8 × 106 m/s in the -y direction is 25 cm from the wire. What is the magnitude and direction of the force on the charge at this instant? (Solutions)

Applets and Animations
 Magnet and Compass Ever wonder how a compass worked to point you to the Arctic? Explore the interactions between a compass and bar magnet, and then add the earth and find the surprising answer! Vary the magnet's strength, and see how things change both inside and outside. Use the field meter to measure how the magnetic field changes. Magnetic Bar Field The Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. Charge in a B-Field The Charge In B-Field model simulates moving charged particles in two identical magnetic field regions separated by a zero magnetic field gap. Three Current-Carrying Wires The Three Current-Carrying Wires model is a ranking task exercise involving the ranking of the current magnitudes in three parallel current-carrying wires.  The simulation displays the net force on each wire because of the other two wires. Magnets and Electromagnets Explore the interactions between a compass and bar magnet. Discover how you can use a battery and wire to make a magnet! Can you make it a stronger magnet? Can you make the magnetic field reverse? Magnetic Field of a Current-Carrying Wire This applet simulates an experiment concerning the magnetic field of a straight current-carrying wire. A large current passes through a vertical wire. You can reverse the direction of this current by using the red button. Rail Gun The Rail Gun Model simulates a rail gun created by running current through long rods generating a magnetic field that accelerates a current-carrying cross-rod. The simulation shows the generated magnetic field. Helmholtz Coils The Helmholtz Coils Model shows a the magnetic field between two circular coils of wire.  The default configuration, known as a Helmholtz coil, sets the separation distance D equal to the coil radius R.  These values produce a nearly uniform magnetic field B between the coils