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This text is meant to accompany class discussions. It is not everything there is to know about uniform circular motion. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations. See the links below.
Click for the questions that go with this reading
Magnetic Force


This video can be found on YouTube at


According to Ampere's Law the flow of charge generates loops of magnetic field.

But what would happen if this wire was placed in the magnetic field of some other source?

The two magnetic fields would interact with each other. When two fields inteact with each otehr they push and pull the field sources. Like when two permanent magnets push apart from each other or are attracted to each other. This magnetic force can be calculated.

The force of attraction comes from

Fmagnetic= force of attraction or repulsion. Measured in Newtons [N.]
B = strength of the external magnetic field. Measured in Tesla's [T.]
I = current in the wire. Measured in Amps [A.]
L = length of the wire that is in themagnetic field. Measured in meters [m.]
θ = acute angle between the current and b-field's directions.
      ("Acute" means less than 90°.)

This equation yields the magnitude of the magnetic force. It does not determine the direction. The direction is determined by the "open right hand rule."


Open Right Hand Rule

The video below explains the right hand rule and gives some examples of how to use it.

This video can be found on YouTube at


Put It Another Way


Watch this vieo to see anohter way to describe the magnetic force.

This video can be found on YouTube at

Now there are two ways to express the magnetic force. Choose the one that matches the unknowns.



Try the problem before clicking on the solution below.

Click here for the solution

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by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)