# Electric Field, Mass, Length

I believe the following are all true for an observer in a different inertial frame :

An object's length is contracted in the direction of its motion
An object's mass increases under motion
The strength of an electron's field is reduced in the direction of motion
The strength of an electron's field is increased orthogonally to the direction of motion

Have I got this right ? If so, is there a connection between the mass increase of an object and the field increase of an electron ?

E.

it isnt exactly mass increase.It is just energy that increases inertia

Meir Achuz
Homework Helper
Gold Member
Also the E and B fields of a moving electron are more complicated.

Indeed, the important thing to remember about electromagnetism is that E and B are not true vectors. Their representations in terms of vector potential, A, are true however, and transform correctly under special relativity.

is there a connection between the mass increase of an object and the field increase of an electron ?
Quite likely. There's a few published papers around discussing how when two (or more) charges are held nearby one another (changing the total energy of the system), you can even uncover the mechanism by which the weight of the system changes (basically, in an accelerated frame, each electron's asymetric field results in an unbalanced inertia-like force).

pervect
Staff Emeritus
I believe the following are all true for an observer in a different inertial frame :

An object's length is contracted in the direction of its motion
Yes.
An object's mass increases under motion
This is ambiguous as stated. Invariant mass does not change with motion. Relativistic mass does change with motion. See the usual FAQ's.
The strength of an electron's field is reduced in the direction of motion
Most likely wrong. If you have two observers at the same point in space-time that are moving relative to each other, the parallel component of the E-field will not change. You may be thinking of a different scenario. See for instance http://www.phys.ufl.edu/~rfield/PHY2061/images/relativity_13.pdf

The strength of an electron's field is increased orthogonally to the direction of motion

Yes, as per the above link, with the same scenario (two obsevers in relative motion at the same point measure how the E-field transforms).

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