Cells operating reversibly and irreversibly

Provided the argument is restricted to what happens at the electrodes, the Daniell cell can also be used to demonstrate what is meant by a cell operating reversibly and operating irreversibly. 

The Daniell cell, an opposing second cell and a galvanometer are joined up in series in a complete circuit. The galvanometer is present to demonstrate whether a current is flowing and, if so, the direction of the flow of electrons. 

This type of experiment defines the conditions for reversibility. 

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