The principle of magnetic attraction and repulsion works in:

Moving Iron Instruments (MI instruments): 

The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. Moving iron type instruments are of mainly two types. Attraction type and repulsion type instrument.

Attraction Type:

• Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. The force of this attraction depends upon the strength of the magnetic field.
• If the magnet is electromagnet then the magnetic field strength can easily be increased or decreased by increasing or decreasing current through its coil.
  Accordingly, the amount of attraction force acting on the piece of iron would also be increased and decreased.
• The attraction type moving iron instrument was developed depending upon this phenomenon. 

​Repulsion Type:

• Whenever two pieces of iron are kept side by side and a magnet is brought nearer to them the iron pieces will repel each other. This repulsion force is due to the external magnetic field. This repulsion force increases if the field strength of the magnet is increased.
• If the magnet is electromagnet, then magnetic field strength can easily be controlled by controlling input current to the magnet. Hence if the current increases the repulsion force between the pieces of iron is increased and it the current decreases the repulsion force between them is decreased.
• The repulsion type moving iron instrument was developed depending upon this phenomenon.