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

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​Please find below the solution to the asked query  

​​The electric pen is a device used for duplicating handwritten documents and drawings. It was discovered by Thomas Alva Edison.
Principle of electric pen: It makes use of electricity. The pen is attached to a wet cell battery which in turn is attached to an electric motor. When current is passed through it, the pen makes 50 punctures per second.

An electric pen is a device made from electrolysis of potassium iodide solution. A solution of potassium iodide, starch and phenolphthalein is made. Two or three filter papers are soaked in this solution and then kept on an aluminium sheet which acts as one of the electrodes. It is connected to negative terminal of the battery using a lead and clip. Another lead is connected to positive terminal of the battery. The power lies between 6 to 12 V. When the power is switched on, the lead connected to positive terminal can be used for writing on the filter papers kept on aluminium sheet. The iodide ions form the solution get oxidized at positive terminal of the battery to form I2which forms a complex with starch in the solution due to which the writing appears blue/black.  
Hope this information will clear your doubts about the topic.   
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