Polarity of an electromagnet

There are some simple rules to help you find out which end of an electromagnet is north and which is south.
(a) Direction of the current round the ends of the coil of wire (Physicists call a straight coil of wire a solenoid).

Look at the ends of the coil from the outside; the direction of the current follows the direction of the letters N and S for north and south (see Figure 1).

(b) the right hand grip rule

(i) for a solenoid
If you imagine gripping the solenoid with your right hand so that your fingers follow the direction of the current then your thumb will point towards the NORTH end of the electromagnet (see Figure 2).

(ii) for a straight wire
If you imagine griping the wire with your right hand with your thumb in the direction of the current then your fingers will show the direction of the magnetic field round the wire pointing from NORTH to SOUTH.
(See Figure 3)