What should I know?

1. There are two types of electric charge: positive and negative. Two charges of the same type repel each other. Two charges of the opposite type attract each other.
2. A charge creates an electric field around it which applies a force on other charged particles that varies with the type and size of the charges and also the distance between them. The field can be either attractive or repulsive, based on the similarities and differences of the charges.
3. The attraction and repulsion of charges is called an electric force. The size of the electric force is determined by a formula -- called Coulomb's law -- that looks analogous to the law of universal gravitation. It is this electric force that holds atoms together.
4. The smallest amount of each charge that you can have is a single positively-charged proton and a single negatively-charged electron. Though a proton is much more massive, an electron has the same amount of negative charge as the proton has positive charge.
5. Charge is measured in Coulombs. One Coulomb represents the total charge of 6.25 billion billion electrons.
6. Like energy, electric charge cannot be created or destroyed. This is the law of conservation of charge.
7. When there are equal amounts of negative and positive charge, their effects are cancelled out -- there is no net charge, and no electric field is produced.
8. Just like masses in a gravitational field, charged objects can have potential energy in an electric field. We will call this electric potential energy. Like charges built up in a small region have electric potential energy based on their proximity to other like charges. Unlike charges that are separated by some distance also have electric potential energy based on their distance from those other charges.
9. One difference between the ways that we talk about gravitational and electric potential energies is this: we nearly always talk about a single object having gravitational potential energy, but there are usually many, many electric charges that have similar electric potential energies. As a result, it is often easier to talk about the amount of electric potential energy per Coulomb of charge. This concept is, somewhat confusingly, called electric potential.
10. Electric charge naturally and spontaneously flows from a high electric potential to a low electric potential. When discussing the differences in electric potential, the term voltage is used.
11. Since protons are bound to the nuclei, they typically are stationary in solids. Despite the common conventional descriptions used by engineers and electricians, a flow of charge is nearly always a movement of electrons.
12. Conductors are materials that allow charges to flow relatively easily from one region to another. The amount of energy needed to get electrons to move away from their atoms is relatively small.
13. Insulators are materials that resist the flow of charges. The amount of energy needed to get electrons to move away from their atoms is relatively large -- so large that it does not often happen.
14. Generally metals are good conductors and poor insulators and nonmetals are good insulators and poor conductors.
15. Some metals occupy the middle ground, being neither a good conductor nor a good insulator. These metals are called semiconductors and are fundamental to most electronic components.
16. Given a voltage between two objects, meaning a difference in the electric potential energies per Coulomb of charge in each of the objects, electrons will flow from one object to the other when brought into contact.
17. If the voltage is large enough, electrons can be made to jump across a insulating boundary between the two objects, such as an air gap, in a phenomenon known as a spark.
18. Electrons can be made to flow from one place in an object to another place in the same object by placing those electrons in an electric field. This process is called induction.
19. When insulators build up charges or are forced to give up charges, they hold onto this overall charge. They only become neutral again by a transfer of electrons into or out of the insulator, as described here: a negatively-charged insulator will need to give electrons to other objects or substances; a positively-charged insulator will take electrons from other objects or substances.
20. When a voltage exists between two regions and a path between these two regions exists, charges will flow. The rate of flow of charge is called the current, which is measured in Coulombs/sec or Amperes (more commonly referred to as Amps).
21. How much current exists depends not only on the voltage but also on the electric resistance the conductor offers to the flow of electrons. Resistance can be thought of as a type of electric friction, hindering electrons as they attempt to move through a material. The amount of resistance in an object is measured in Ohms, which is symbolized with a capital omega, 𝝮.
22. Electric current is the result of a voltage being applied through a substance with an electrical resistance. This empirical relationship is known as Ohm's law, which is commonly stated I = V / R.
23. An electric circuit is any path along which electrons can flow. There are three types of circuits: a series circuit forms a single pathway for electron flow; a parallel circuit forms branches - each is a separate path for the flow of electrons; and a series-parallel circuit, which is the most common and has some components in series and some in parallel.
24. The equivalent resistance of a circuit is the total resistance that charges feel exists between them and the other end of the circuit. The series equivalent resistance is simply the sum of the individual resistances -- a number that is greater than each individual resistance. The parallel equivalent resistance can be less than the sum of the resistances of each individual resistor, because fewer charges are moving down each branch and therefore encounter fewer interactions between them and the other traveling charges.
25. Each component in a circuit consumes a certain amount of the voltage. This voltage consumption is called a voltage drop. For a series circuit, the sum of the voltage drops is equal to the source voltage. For parallel circuits, the source voltage is applied equally to each branch -- thus the voltage drop on each branch is the same as the source voltage.
26. Voltage drops can be measured in a live circuit by connecting a voltmeter in parallel across the component.
27. The current moving through a component can be measured by connecting an ammeter in series in a live circuit just ahead of the component.
28. The rate at which the energy of the traveling electrons is converted into another form is called electric power. Like any other type of energy, the power is the amount of energy used or converted per second, P = E / t. A handy shortcut for finding the electric power used by a particular component is the product of the current going through the component and voltage drop at that component, P = I V. No matter how it is calculated, electric power is measured in Watts (W).
29. As consumers the power we buy from a power plant does not add or remove electrons to or from the circuits in our homes. Instead, we are purchasing voltage, which moves those electrons back and forth, doing work on our electrical components.
30. As electrically-charged objects move, they produce a magnetic field. There is no magnetic field produced by a stationary charged object.
31. Like electric fields, magnetic fields can interact, transmitting a force through the space around a magnetic object. Magnetism is also a field force.
32. Like electric fields, magnetic fields can either attract or repel.
33. Like electric charges, there are two types of magnetism: a north pole and a south pole. Unlike electric charges, every magnetic object must have both a north and south pole. A magnetic monopole has never been observed.
34. The atoms of some elements -- iron, nickel and cobalt -- produce magnetic fields due to the aligned spins of their unpaired electrons.
35. In microscopic regions of objects made of these materials, the magnetic fields of individual atoms align, forming magnetic domains.
36. When the magnetic domains of an object are aligned, that object is magnetized. The strength of the magnet is due, in part, to the amount of alignment of these domains.
37. When electrons move through a wire, they induce a magnetic field around the wire. When a magnetic field moves over a wire, in induces an electric current on that wire. These phenomena are grouped together under the name electromagnetic induction.
38. Both electric motors and electric generators work because of induction -- because a magnetic field can cause charges to flow and because flowing charges apply a magnetic force.