Induction is another way to create a charge in an object. You can charge an object by induction without even touching it. I’ve got a couple of really neat experiments that will show you how this works, but here’s the basic idea: when you have two metal objects, like two soda cans, standing upright on a foam slab and just touching each other (so they are insulated from the table but in contact with each other), you can bring a charged balloon close to one of them and see a really interesting effect: the can closest to the charged balloon (which has a negative charge) will take on a positive charge, and the soda can furthest from the balloon will take on a negative charge. And when you separate the two cans, the charges on each will be evenly distributed over the surface of each can and remain polarized (the further can keeps its negative charge and the closer can keeps its positive charge). That’s charging by induction!

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Note that the net charge of the system was zero when you started, and is still zero when you finish, even though the electrons have moved and the charge on each can is different than when you started. Charge cannot be created or destroyed, however it can be transferred from one object to another by electrons. If you touch the soda can while you’re charging it, the electrons will enter your hand and “go to ground” and discharge your system. Humidity also does this using water vapor – the water molecules will dissipate your static charge build up so it looks like your static electricity experiments don’t work! However, if you bring a positively charged object near the soda cans and then touch the can, electrons will be attracted and actually create a larger static charge on the can.

This idea of “grounding” simply means that the excess charge (either positive or negative) can be removed by transferring electrons from something really big, like the Earth, that acts like a huge ocean of electrons.

Click here to go to next lesson on Electroscope.

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