Magnetism

 Motion of Charged Particles in Magnetic Fields

 Whiteboard

 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
 Q1: On your whiteboard, make four illustrations of the electrons' path inside the dotted region, 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 Comparing the motions of two different particles in one magnetic field Here, a uniform magnetic field is directed into the paper.  A hydrogen ion (a proton; shown to the left as +q) and an alpha particle (two protons plus two neutrons; you get to draw it) 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. Q2: 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.

 References

 Arons, A. (1996), Teaching Introductory Physics, Wiley: NY, p. 105. Cutnell, J. and Johnson, K. (1998), Physics, Vol. 2, Wiley: NY, p. 634-6.

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