Table of Contents
Electricity in Physics
Electrical energy is the movement of electrons between objects. As electrons are a form of matter, they are held by the law of conservation of matter and cannot be created nor destroyed. So, one can add and remove electrons between objects to transfer electrons.
If an atom has an imbalance of charge1), the atom is a charged atom. All items wish to be neutral. Typically, this means an electrical equilibrium if true neutrality is not possible.
Opposite charges attract, and like charges repel. Remember than an electron's symbol is $e^-$, it has a negative charge, so removing electrons make an object positively charged, and adding electrons make an object negatively charged.
Ground
A ground is an electrical connection to the earth2)3). It acts as an easy path for excess or lacking electrons to transfer in and out of the system to neutralize.
Types of Objects
Objects are typically in a spectrum between conductor and insulator. Conductors transfer electrons well, while insulators resist electron movement.
- Conductors hold onto electrons weakly
- Insulators hold onto electrons strongly
Good conductors are typically metals, while good insulators are typically plastics, rubber, or other nonmetals like air. For the purposes of physics, you can ignore the fact that there is a spectrum and treat all objects as black or white conductors or insulators.
Contacting Charged Objects
When two objects with different charges contact, a transfer of electrons will occur. 
| Object 1 | Object 2 | Resultant Charge |
|---|---|---|
| Positive | Positive | Positive4) |
| Negative | Negative | Negative5) |
| Positive | Negative | ??6) |
| Positive | Neutral | Positive7) |
| Negative | Neutral | Negative |
| Neutral | Neutral | Neutral |
This form of electrical transfer is called “Charging by Conduction”.
Contacting Neutral Insulators with a Charged Object
As insulators tend to avoid electron transfer, only the polarity of the neutral object is changed upon contact. This is true for a positive or negative charge. With a polarity change, the electrons in the object rearrange to satisfy the rule that opposite charges attract and negative charges repel. Charges of either object does not change!
Charging by Induction
A charged object can affect the polarity of surrounding objects even without direct contact, think of it as similar to the above section. If a ground is connected to an object polarized by a nearby charged object, electrons will transfer in/out between the ground and the polarized object as a result of the electron attraction from the charged object. If the ground is then disconnected before the charged object is moved away, the electrons in the polarized object will remain, thus charging the object8). This is induction charging, and it works with both positively or negatively charged objects.
| Charged Object | Polarized Object | Resultant Charge of Polarized Object |
|---|---|---|
| Positive | Electrons will rush into the polarized object from ground as they are attracted to the nearby charged object | Negative |
| Negative | Electrons will rush out of the polarized object into ground as they are repelled by the nearby charged object | Positive |
Electrostatics
Both positive and negative charges can move between objects. For an explanation of positive charge movement see below.
- Positive charges can move
- Protons can't move
- Protons are the mass while the positive charge is an electron deficiency
Coulomb's Law
Coulomb's law in terms of physics allows one to correlate the amount of charge, radius, and a constant with the resulting force between the particles.
- $F_e = \frac{kq_1q_2}{r^2}$, where
- $F_e$ is the resultant force in Newtons
- $k$ is $9 \times 10^9$9)
- $q_1$ and $q_2$ are the charges of the particles in Coulomb (C)
- electron = $-1.6 \times 10^{-19}$ C
- proton = $1.6 \times 10^{-19}$ C
- $r$ is the radius (distance) in meters
