What is the basic principle of electric pen ? Explain how it can be used for writing

What is the basic principle of electric pen ? Explain how it can be used for writing.
A. Electric charge on ions is used for writing with an electric pen.
Method :
(i) Take a filter paper soaked in potassium iodide solution to which a pinch of starch is added.
(ii) Place the filter paper on a metal sheet.
(iii) Connect the negative terminal of battery to the metal sheet.
(iv) Write on the paper with the end of the wire connected to the positive terminal.
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(v) The writing appears on the paper. This happens because the when current is passed, the K+ ions are attracted to the metal sheet. The iodide ions (I) react with starch to turn blue black.