Please Help! b) For a charged particle moving in the presence of a magnetic fiel

Question

Please Help!

b) For a charged particle moving in the presence of a magnetic field, equation (1) in the handout was obtained starting with the fact that the centripetal force on a particle moving in a circular orbit is equal to the magnetic force on that particle. Use this information to rank the particles in order of the speed at which they are moving. c) What might account for the spiraling effect, i.e. a circle with a radius that decreases with time, as displayed by particles 1 and 2? 3) The figure shows tracks of particles resulting from an event that begins at point A. A radioactive source traveling from the left produces the three charged particles as shown. Particles 1 and 2 produce the two spiral tracks. Particle 3 moves forward, producing the long track with slight upward curvature. Each of the three particles has the same mass and carries a charge of the same magnitude. A uniform magnetic field is directed out of the paper toward you. a) Use your knowledge about the force on a charged particle in the presence of a magnetic field and the vector properties of: F = qv x B to deduce the charge on the particles 1 - 3 in the figure.

Explanation / Answer

PART A:

Particle 1 is a negative charge, as it satisfies the left hand rule.

Particle 2 is a positive charge, as it satisfies the right hand rule.

Particle 3 is a negative charge for the same reason as particle 1.

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PART B:

Note that

R = mv/qB

Thus, larger velocity means larger radius.

Thus,

1. Particle 3 is fastest.
2. Particle 2 is second fastest.
3. Particle 1 is slowest (but just slightly slower than particle 2.)

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R increases with time; As R increases with decreasing B, thus, B might be decreasing with time. [ANSWER, PART C]

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