# Positron movement in a coil-induced magnetic field

#### wgas

in a microscopy class:
problem is to illustrate the path of a positron on both sides of the axis in a coil produced magnetic field. consider both cases of the particle's velocity and the magnetic field being a)in the same direction & b)in opposite directions.

i have no clue. any help? would it just be the opposite of an electron's path?

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#### Shooting Star

Homework Helper
Do you know anything about the electron path? You should write something about that, at least.

#### wgas

see attached pic.

where A & B are condenser lenses in an EM, so they are fields generated by a coil.
A) the field & the velocity are the same direction
B) they are opposite
(both only shown on one side of the axis).

is this correct , with the electron in blue & the positron in red?

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#### Shooting Star

Homework Helper
As far as I understand from your diagram, the dotted line represents the axis of the coil, and the e-/p+ is travelling in a st line inside the coil. Just outside the coil the magnetic field has started to diverge away from the axis, and you have drawn the instantaneous force on the e-/p+. The path of the particle inside the coil is above the axis.

In fig A, the B would point slightly upward and remain in the plane of the paper just outside the coil. For a +ve q, the force would be only out of the paper toward you, with no “down” component. Remember, these are just the instantaneous forces on the particles when the field lines are not parallel any more, not the trajectories. After an instant, there will be a “down” component to the force, but I’m not very sure how the full path is going to be. I have to read up on electron microscopes.

The same goes for fig B. The “out” and “in” are correct.

#### wgas

ah. thanks for the help.

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