## Why does horizontal velocity of electron slow down when moving in an electric field?

1. The problem statement, all variables and given/known data

This is from "Special Relativity" by A.P. French. Chapter 1.

"An electron is moving with speed 0.5c in the x direction enters a region of space where there is a uniform electric field in the y direction. Show that the x component of the velocity of the particle must decrease. "

3. The attempt at a solution

1. Is it because there is acceleration in the y-direction, the electron will emit radiation, hence losing energy/mass? But what has this got to do with relativity?

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 Quote by unscientific 1. The problem statement, all variables and given/known data This is from "Special Relativity" by A.P. French. Chapter 1. "An electron is moving with speed 0.5c in the x direction enters a region of space where there is a uniform electric field in the y direction. Show that the x component of the velocity of the particle must decrease. " 3. The attempt at a solution 1. Is it because there is acceleration in the y-direction, the electron will emit radiation, hence losing energy/mass? But what has this got to do with relativity?
I don't think that's what the author is getting at. Suppose the acceleration is small enough so that you can ignore energy lost via radiation.

Look at what happens classically.

 Quote by SammyS I don't think that's what the author is getting at. Suppose the acceleration is small enough so that you can ignore energy lost via radiation. Look at what happens classically.
Well..the acceleration is only in the y-direction so the x-component of the velocity remains unchanged while the vertical velocity is increasing?

## Why does horizontal velocity of electron slow down when moving in an electric field?

it's an electric field. Ask yourself this "Is the acceleration always only in the y direction?"

 Tags relativity electron