Changing polarity on demand

[nullexception]

I have two pieces of metal which I am using as some form of gate.When I want to open the gate,the two metals should have like poles so as to repel and hence open the gate.

When I want to close the gate the two metals should have unlike poles.

How can I make any metal have only a polarity of my choice?

 

[barry]

Are you talking about electromagnets? First of all, this won't work with "any metal", it must be a ferrous metal. By simply reversing the direction of current flow you'll change the polarity

 

[nullexception]

Yes I am talking about electromagnets.

 

[chuckey]

Magnetism works over a short range. If you are talking about something like a garden gate, forget it. If you are talking about the gate moving 20mm,, it will be possible although you will need a lot of power. A motor driven solution might be better.
Frank

 

[Gorgon]

Use a DPDT relay to change the polarity of one of the magnets.