How can a thin layer of …

The process of depositing a thin layer of any superior metal over an object of a cheaper metal, with the help of electric current is called electroplating.
For example; deposition of silver on brass or copper objects and that of copper, nickel, chromium etc., on objects made of iron is done by electroplating.

The experimental set up for electroplating copper on any object, such as a metallic spoon can be summarised here;

-The object to be electroplated, say iron spoon is made cathode(-ve electrode).

- A thin sheet of pure silver is made anode (+ve electrode).

-An acidified solution of silver cyanide(AgCN) is used as the electrolytic solution.

When electricity is passed through the solution, (AgCN), (Ag+) ions moves towards the anode and get reduced to silver metal. The silver metal gets electroplated on the object,i.e, metallic spoon.

The silver ions (Ag2/4+) moves towards
cathode. Here (Ag2/4+) ions do not get oxidised to Ag2+ ions. These silver ions (Ag2+) ions go into the solution. As a result of this reaction at the anode, concentration of (Ag2+) in the solution is maintained.