Charge

Electrical charge is an inherent property of matter, just like mass. When an object with an electrical charge is placed near a net charge source, it will interact electromagnetically with that source similar to how an object with mass will interact gravitationally with another object that has mass. Electrical charge is measured in Coulombs(C).

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However, gravitational forces are always attractive: if you put two objects with mass near each other, they'll always go towards each other. Electrical charges can be of two signs which allow them to be attractive or repulsive.

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The simple way to remember how two charged objects will interact is through this:

Opposite charges attract, like charges repel. Therefore, a negative charge will always attract with a positive charge but negative charges repel other negative charges and positive charges repel other positive charges.

Usually, negative charges are represented by electrons with an electrical charge of -1.60 * 10^-19 Coulombs(C) while positive charges are represented by protons with an electrical charge of 1.60 * 10^-19 Coulombs(C). When charged objects interact, usually it is the electrons that move around and attract and repel with other protons and electrons, respectively. Protons are bound to atomic nuclei through the strong nuclear force, so they won't move freely through objects unlike electrons, which float around in atomic orbitals.

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One important concept to know about the charge is that the net charge is always conserved in an isolated system. This is elaborated on in this article later.

An electrical conductor is simply a material that allows for electrons to move through it very freely. Examples include pretty much most metals and seawater. An electrical insulator is simply the opposite of an electrical conductor; it is a material that doesn't allow for electrons to freely flow through it. Examples include wood, glass, air, and plastic.

Charging by conduction is when you add or subtract charge to electrically charged objects by putting them in physical contact with one another. Remember that the protons in an object won't move so all of the electrostatic interaction will happen due to electrons. If you put two objects in physical contact, the objects will try to achieve electrostatic equilibrium, where they bear equal charge. This means the object with more electrons will give away electrons so that its charge will increase(since an electron's charge is negative) and the object it's giving electrons to will lose charge. Thus, the more negative object becomes more positively charged while the more positively charged object will become more negatively charged. In the end, both objects will carry an equal charge and if you add up the charges of the objects in equilibrium since the total charge is conserved, it will equal the total charge in the system before they touched, assuming no other surfaces took charge from either object.

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Charging by conduction is why if you take a balloon and rub it against a sweater, the balloon, which is less negatively charged than the sweater, will take the sweater's negative charge and become more negatively charged itself. This will allow the sweater to be positively charged and the system to be in electrostatic equilibrium.

Charging by conduction is also the underlying principle behind static electricity. If you ever rub your feet on a carpet, you start to build up negative charge so that if you touch another human who likely didn't rub their feet, the net negative charge in your body will discharge through the other human and you'll both feel a shock. You can try this at home if you want as the shock isn't too harmful but you still want to be careful.

It is possible to alter the electrostatically polarize an object without actually touching it. This won't change its total charge but it will certainly change its distribution of charges and polarize them.

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For a simple reference definition, polarization is when an object's charge is conserved but its charges are distributed such that one side is strongly positive and one side is strongly negative, rather than the entire object having an equal charge.

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If you charge by induction, you basically make it such that putting two charged objects near each other will cause their charge distributions to change. Let's use an example to illustrate:

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If I have a negatively charged rod and put it to the left of a stationary neutral charged sphere, the electrons in the sphere will repel from the electrons in the rod, causing the electrons in the sphere to all pile up on the right side of the sphere while the left now only has protons. This causes polarization of the sphere's charge as the sphere has a net negative charge on one side and a net positive charge on the other.

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You can apply this to similar systems if you remember that depending on the net charge of the object being brought, the electrons will interact such that electrons will either pile up on the side next to the rod if the rod is positively charged or electrons will pile up on the side opposite the rod if the rod is negatively charged.

Charging by grounding is when you take something with an excess negative or positive charge and you plug it into the ground in order to neutralize it. By grounding the object, you're connecting it to the entire Earth, which has a neutral charge. By doing this, the object loses all of its excess charge to the massive Earth and then gets a net 0 charge itself.