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Let's say I have two iron plates (P1 and P2). I want one side of each plate to have an opposite charge.
The surface of P1 should be charged with a positive charge and that of P2 with a negative charge so when I bring the charged sides of two plates closer they should attract eachother. But inorder to achieve this there must be way to charge the plate surfaces with opposite charges. How do I electrostatically charge the plates?

It would be desirable if I can charge the plates using electricity (AC or DC).

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  • $\begingroup$ What voltage do you want the plates to be charged to? What is the charge going to be used for? $\endgroup$
    – hdhondt
    May 20 '20 at 10:12
  • $\begingroup$ @hdhondt I've not decided yet the voltages to use. I first wanted to know if its possible to charge the plates and methods to do so. $\endgroup$
    – Somanna
    May 20 '20 at 10:21
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    $\begingroup$ In that case, a battery or any DC source will do the trick, as explained by the answers. $\endgroup$
    – hdhondt
    May 21 '20 at 4:57
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You can charge the plates by applying a potential difference across them. You can do this using any voltage source, including a battery or an AC source.

The charge in an ideal parallel plate capacitor in air is given by $$ Q = \frac{\epsilon_0A}{d}V$$ where $\epsilon_0 = 8.854\times10^{-12}\,\text{F/m}$ is the permittivity of free space, $A$ is the plate area, $d$ is the separation of the plates and $V$ is the potential difference between the plates. Thus the wider the plates are, the higher the voltage and the closer the plates are when you charge them, the greater the charge induced.

You can charge the plates simply by momentarily connecting the positive terminal of the battery to P1 and the negative terminal to P2, and then disconnecting the battery without touching the wires with a conductor (otherwise you might discharge the plates).

If you need more charge and hence higher voltage than what a battery can provide, you could use AC voltage such as the mains (only if you know what you are doing!), which would get you to 156 to 340 V depending on where you live. You would use a diode to keep the plates from discharging as the voltage polarity changes. You would connect one terminal of the AC voltage source to P2, the other terminal to the anode of the diode and the cathode to P1. Finally you would disconnect the voltage source as before.

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The plates can be charged using a dc source. The whole scenario is very similar to charging a parallel plate capacitor using a constant voltage source like a battery.

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