a simple cell typically has plates of copper (cu) and zinc (zn) in dilute sulphuric acid. the zinc dissolves and bubbles of hydrogen appear on the copper plate. these hydrogen bubbles interfere with the passage of current so a simple cell can only be used for a short time. to provide a steady current, a depolarizer (an oxidizing agent) is needed to oxidize the hydrogen. in the daniel cell, the depolarizer is copper sulphate, which exchanges the hydrogen for copper. in the leclanche battery, the depolarizer is manganese dioxide, which oxidizes the hydrogen to water.