The Motion of Charged Particles in Magnetic Fields

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The motion of an electron in four different magnetic fields

An electron is moving with a velocity v in the direction shown in the illustration.  The electron enters a uniform magnetic field B directed out of the page, marked by the dotted lines as shown.

1) On your whiteboard, make four illustrations of the electrons' path, one for each of the following field strengths:
   (a) B = 0 inside the region marked by the dotted-line
   (b) weak B field inside the region marked by the dotted-line
   (c) medium strength B field inside the region marked by the dotted-line
   (d) very strong B field inside the region marked by the dotted-line

[Solutions][Right-Hand Rules]

Comparing the motions of two different particles in one magnetic field
 

Here, a uniform magnetic field is directed into the paper.  A hydrogen ion and an alpha particle (both shown to the left as +q) enter the field having the same velocity.  Assume the field is large enough so that the particles can execute complete circular trajectories within the field.

2) On your whiteboard, calculate the relative sizes of the two circular paths and sketch them to scale showing the direction of travel for each.  Recall equations for centripetal acceleration and force.  Give explanations for your reasoning.

[Solutions][Right-Hand Rules]

References:

Cutnell, J.and Johnson, K. (1998), Physics, Vol. 2, Wiley: NY, p. 634-6.

This page contributed to by Camilo Tafur and Dan MacIssac