Fill in the following blanks with suitable words:
(a) The lines of _____ round a straight-carrying conductor are in the shape of _____
(b) For a current-carrying solenoid, the magnetic field is like that of a _____
(d) The magnetic effect of a coil can be increased by increasing the number of _____, increasing the _____ or inserting an _____ core.
(e) If a coil is viewed from one end and the current flows in an anticlockwise direction, then this end is a _____ pole.
(f) If a coil is viewed from one end, and the current flows in a clockwise direction, then this end is a _____ pole.