That's all down to the power of the field and the sensitivity of your measuring intrument.
A Magnetic Force
no. Eris does not have a magnetic field
Curl the fingers of your right hand into the palm and extend the thumb. The thumb indicates the direction of the current, and the direction of the fingers indicates the direction of the magnetic field.
Magnetic field is made up of magnetic lines.
The magnetic field lines are arranged circularly around the wire.
Less than 1 AU for sure!
They extend between the North and South MagneticPoles.
As far as the electric field is stationary then no magnetic field. But when electric field is moving at a uniform speed then a magnetic field will be produced. This is what we call Lorentz magnetic field.
Planets are too far from each other to have any observable interaction of their magnetic fields.
no mars magnetic field is not strong because it is far away from the sun than earth.
Because it is far too small to have any effect. The Earth's magnetic field is thought to be generated thousands of miles underground by moving rivers of iron.
A Magnetic Force
Magnetic freild
As far as I know, in a magnetar, which is a special type of neutron star.
How far away? Compasses function based on their interaction with the Earth's magnetic field. If a person were to take a compass outside of that field, it would cease to provide any relevant information. Of course, no human has ever been anywhere near that far away, but interplanetary robots and probes have.
The outermost layer is called the Corona and it extends deep into the Solar System (the Earth is actually within it). Beyond that there is the Sun's magnetic field and of course gravity goes on forever, just getting weaker and weaker.
Any charged particle in motion especially not parallel to the magnetic field, current carrying conductor kept inclined or perpendicular to the magnetic field would get deflected. As far as electric field is concerned, even stationary charges would be displaced.