Question

1).which of the following describes the interaction between a south pole and a north pole of a magnet

a) attract
b) repel
c) stay unchanged
d) it depends

2). which of the following producing a magnetic field
a) motion of electrons
b) pair of atoms
c) magnetic area
d) static charges

Answer 1

1) a) attract

The magnetic force between two magnetic poles is attractive for two unlike poles and repulsive for two like poles. Therefore we have:

1- For two north poles, the force between them is repulsive

2- For two south poles, the force between them is repulsive

3- For a north pole and a south pole, the force between them is attractive

In this problem, we are in the situation described in 3), so the force between the poles is attractive.

2) a) motion of electrons

While electric fields are produced by static electric charges, magnetic fields are produced by charges in motion (currents). In particular, a current in a wire (where a current is simply the motion of electrons inside the wire) produces a magnetic field whose intensity is

`B=(\mu_0 I)/(2 \pi r)`

where

I is the current in the wire

r is the radial distance from the wire

And the direction of the field lines are such that the field form concentric circles around the wire.