# Can you stop an electron in vacuum?

If we shoot an electron in vacuum tube, then stop it with electromagnetic field, and switch off the field, what will happen with electron?

1. Will it continue its movement?
2. If there is a gravitational force, will it be attracted by it?
3. If there is no gravitational force, will it just hang in empty space?
• What do you think will happen, and why? – Carl Witthoft Dec 2 '14 at 15:42

• An electric field will accelerate/decelerate an electron, depending on the direction of the field.
• A magnetic field will bend/deflect a charged particle.
• If you remove the electromagnetic field, then the electron will continue on its existing path, until it meets the walls of the container, another particle, or another electromagnetic field.
• An electron has a small mass, so it will be affected by a gravitational field, but an electromagnetic field is $10^{39}$ times stronger. This is why the Sun's immense magnetic field is unable to hold on to the solar wind, which accelerates away from it.
• If you remove the electromagnetic field, then the electron will continue on its existing path. How is this possible? I though it is moved by inertia in vacuum? How will it accelerate after complete stop? By what force or energy? Is it self propelled? – Alex Burtsev Dec 2 '14 at 18:12
• Yes, if it decelerates to zero, then it will stop, and be affected only by gravity. By existing path, I meant the path that it was on when the EM field was removed, whatever that may be, and different to its original speed and direction. – iantresman Dec 2 '14 at 18:14
1. Will it continue its movement?

No, it's now stationary1

1. If there is a gravitational force, will it be attracted by it?

Yes

1. If there is no gravitational force, will it just hang in empty space?

Yes, assuming no other forces are acting on it1

1 - Note that it's impossible to get anything perfectly stationary, there will always be some movement due to limitations in your ability to perfectly slow it as well as quantum fluctuations and the uncertainty principle. But for the purposes of your question it is stationary.

The electron having mass will exhibit gravitational attraction and begin moving again, however; unless there is a larger object near the electron to it's nucleus it will orbit around it's original host and eventually regain it's original velocity as long as the Lagrange point is not breached.

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