The reference electrode is essential to Know "what is the exact potential"without variations. The current never must flow for the reference electrode because produce potential drop, for this reason, it use another electrode called contra electrode. By this electrode will go the current, without produce changes of potential in the reference electrode. The electrode of calomelanos it is a good reference electrode.
A reference electrode imply that many researchers use the same electrode of "reference" so that we can obtain comparable results. Do you imagine many electrodes of reference, and many results very different?. How could we understand us?
As mentioned by Carlos, three electrodes are necessary to minimize the potential drop and is absolutely crucial for macro-sized electrodes, however for the case of a microelectrode the currents passed between the electrodes is so small that there is virtually no Ohmic drop and as a result a two electrode system is sufficient.
The design of three electrodes is the best way to have reproducible results and also, avoid damage of the reference electrode.
The third electrode, also called, secondary electrode, mathematically speaking, avoid drop potential this way: Vapp - i R. "I" is the current flowing. This equation shows how the potential drops due to the resistance. .
On microelectrodes "i" is very small, so that, the drop potential is also very small or insignificant. Stanislav has been assertive with this comment.
Regards
Hello Talha,
The answers others have provided are excellent. If yow want further information may I recommend 'Electrochemical Methods: Fundamentals and Applications' by Bard and Faulkner:
http://glearning.tju.edu.cn/pluginfile.php/74331/mod_resource/content/0/%E5%8F%82%E8%80%83%E4%B9%A6/Electrochemical_methods_2ed_2001_-_Bard_Faulkner.pdf
You'll find information regarding the use of a Reference Electrode on pages 25 and 53-54.
Kind regards,
Jules
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