Which variable stars have pulsation periods between 1.5 hours and 1.2 days?
a. cepheid variables
b. protostars
c. rr lyrae variables
d. nebulas

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

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.