Building a consumer electronics company in six months [part one]

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So, What is ELECTRIC CHARGE ?

Electric charge is the physical property (?) of matter that causes it to experience a force when close to other electrically charged matter. There are two types of electric charges – positive and negative. Positively charged substances are repelled from other positively charged substances, but attracted to negatively charged substances; negatively charged substances are repelled from negative and attracted to positive. An object will be negatively charged if it has an excess of electrons, and will otherwise be positively charged or uncharged. The SI derived unit of electric charge is the coulomb (C), although in electrical engineering it is also common to use the ampere-hour (Ah), and in chemistry it is common to use the elementary charge (e) as a unit. The symbol Q is often used to denote a charge. The study of how charged substances interact is classical electrodynamics, which is accurate insofar as quantum effects can be ignored.

Electric charge generates electric field. The electric charge influence other electric charges with electric force and influenced by the other charges with the same force in the opposite direction. There are 2 types of electric charge:

Positive charge (+)

Positive charge has more protons than electrons (Np>Ne).
Positive charge is denoted with plus (+) sign.
The positive charge attracts other negative charges and repels other positive charges.
The positive charge is attracted by other negative charges and repelled by other positive charges.

Negative charge (-)

Negative charge has more electrons than protons (Ne>Np).
Negative charge is denoted with minus (-) sign.
Negative charge attracts other positive charges and repels other negative charges.
The negative charge is attracted by other positive charges and repelled by other negative charges.

Electric force (F) direction according to charge type

q1/q2 charges	Force on q1 charge	Force on q2 charge
- / -	←⊝	⊝→	repletion
+ / +	←⊕	⊕→	repletion
- / +	⊝→	←⊕	attraction
+ / -	⊕→	←⊝	attraction

Charge of elementary particles

Particle	Charge (C)	Charge (e)
Electron	1.602×10-19 C	-e
Proton	1.602×10-19 C	+e
Neutron	0 C	0

Coulomb unit

The electric charge is measured with the unit of Coulomb [C].
One coulomb has the charge of 6.242×10¹⁸ electrons:

1C = 6.242×10¹⁸ e

Electric charge is a component of atoms. In other words, after we have broken an object into molecules, and broken the molecules into atoms, when we break the atoms apart we discover particles of electric charge. Charge is material, it is like atoms but it is one step lower than atoms. Most science textbooks tell us that solid objects are made of atoms. It is also valid to state that solid objects are made of electric charge. Objects are made of equal quantities of positive and negative charge, and objects stay together because of the attraction between the quantities of opposite charge inside them. Chemical bonds are electrical in nature.

Charge flow

When charge moves, what do we call it? Well, if the positive and negative charges move along together, we call it "physical motion." Since matter is composed of charge-carrying particles, all physical motion is a motion of charge, but in most cases both the negative and the positive charges move along as one. On the other hand, whenever opposite charges move separately, that's when interesting things occur. Opposite charges moving along together are "mechanical", while opposite charges moving differently are "electrical." If the negative charge in an object should start moving while the object's positive charge stays at rest, then we call that motion a flow of electricity, or an electric current. The words "electric current" mean the same as "charge flow."

Charge: it's not energy

Charge is not energy. A fixed quantity of charge can possess many different amounts of energy at the same time (and note the same charge in different values of capacitor.) Also, if you know the amount of charge present, you have no knowledge of the amount of energy. Also, charge and energy move differently: in AC cables the charges sit in one spot and slowly wiggle, while the energy flows across the circuit at almost the speed of light. (Insight: charge is different from electrical energy in thesame way that air is different from sound waves.) Inside electric circuits, charge flows slowly in a circle like a drive belt, while energy moves quickly from the source to the load. Some people think that since charge and electrical energy are mysterious and invisible, they must be the same thing. But see below: electrical energy is invisible, but charge is definitely VISIBLE. And finally, J. C. Maxwell points out that charge and energy MUST be two different things, since the amount energy is calculated by multiplying the amount of charge by the voltage of that charge.

If charge is not energy, then what exactly is it? Well, a block of iron can be lifted above the Earth in order to store potential energy, or it can be spun rapidly to store kinetic energy, but the mass of the iron is not the energy being stored. So there's our answer by analogy: "charge" is a concept very similar to "mass." We can store potential energy by forcibly separating the opposite charges in a capacitor, or we can store kinetic energy by forcing the charges in a copper inductor to spin around the spiral windings. But charge stays constant while doing this, and mass stays constant when lifting or spinning an iron disk. (Yes yes Einstein, but at this level of Classical chysics, Relativity is still just a distraction. And, we don't have to double the weight of a flywheel in order to double the KE stored by its spinning motion!)

Charge: not just a property, but also "a stuff."

Charge is just a property, so how can a property move from place to place? Well, the same is true of mass. Mass is a property, but it also behaves like "a stuff" which can be moved around. Fortunately we have a term for properties which act like stuff. They're called "conserved quantities." Mass is a conserved quantity: in order to get rid of mass inside an enclosure, we can't just make it vanish, instead we must take that mass past the walls of the enclosure. Charge is like mass: a conserved quantity, "a stuff." This is very different than non-conserved properties. The color blue is a property of a painted object, but "blue" can easily vanish: just heat the object so the blue is burned to black! Mass and charge are different: we can't easily get rid of them, instead we must remove them. (In more rigorous language, a conserved quantity is one which, in order to change the amount inside a closed "Gaussian" surface, we must pass it through that surface.) So, charge is a "stuff-like" property. It's a mistake to think it's anything like the blue color of paint, or to call it "just a property." 

 

Charge is "poles"

When the positive and negative charges of matter are sorted out and pulled away from each other, "static electricity" is the result. When (+) is pulled away from (-), an invisible force field connects them and causes them to attract each other. This field is similar to magnetism in many ways, but it is not magnetism, it is called an Electrostatic Field, or "e-field." With magnetism, the lines of force spring from the north and south poles of magnets, and these lines seem to connect the opposite magnetic poles together. In Electrostatics, the electrical lines of force connect the (+) and (-) poles together. What is charge? It is the "pole" where the electrical lines of force come to an end. Follow the lines of a static "e-field" along, and eventually you'll arrive at a small bit of "charge." Electric charge is the glue which attaches the flux lines of e-field to the particles of matter.

Charge: it's not invisible

Charge is not invisible. Whenever light bounces off an object, it bounces off the outside of the atom, and the outside of an atom is made of negative charges. In other words, electric charge reflects light. Yet when we rub a balloon on our hair, the balloon (and the hair) don't look different. How can charge be visible if we see no visible difference when we electrify a balloon? Simple: the balloon's excess charge is way too small. The imbalanced charge caused by rubbing a balloon on your head is like a teacup poured into the ocean: it is very tiny when compared to the charge which is already there. The balloon is made of charge, and the amount of charge that is added or removed by the hair is incredibly small. If we could add a billion times more charge to that "charged up" balloon, then we would see some changes in its color. But the poor balloon would instantly explode violently outwards because alike charges on its surface would fiercely repel each other. (Here's a clue: when a significant portion of the positive charges in a block of Uranium become disconnected and fly away from each other, that's called a nuclear explosion.)

Here is a way to see charge directly: look at the surface of a wire. Metals look metallic because they contain a "fluid" composed of movable electrons. This electrical "fluid" is an excellent reflector of light waves, and it causes the surfaces of metals to act like mirrors. It's these same electrons which flow during an electric current. The "silvery" stuff of a metal is the charge. What is charge? It is a "silver liquid" which is found in all metals, and which can be forced to flow. Even though the charge is visible, its flow is not. Look carefully at wires in an operating electric circuit and you won't see anything moving along. This is not very mysterious: stir a glass of water and then look for the flowing motion. You'll see moving bubbles and perhaps moving specks of dirt, but you won't see the water move. The silvery charge-fluid in a wire has no bubbles or dirt, so even though the charge is visible, we cannot tell if it is moving or still. 

The diagram below shows a lithium atom with its 3 electrons and 3 protons (and three uncharged neutrons). Also shown is a positive lithium ion, positively charged because it is missing one of its electrons, and a negative lithium ion, negatively charged because it has an extra electron. 

Conservation of electric charge

The total electric charge of an isolated system remains constant regardless of changes within the system itself. This law is inherent to all processes known to physics and can be derived in a local form from gauge invariance of the wave function. The conservation of charge results in the charge-current continuity equation. More generally, the net change in charge density ρ within a volume of integration V is equal to the area integral over the current density J through the closed surface S = ∂V, which is in turn equal to the net current I:

Thus, the conservation of electric charge, as expressed by the continuity equation, gives the result:

The charge transferred between times and is obtained by integrating both sides:

where I is the net outward current through a closed surface and Q is the electric charge contained within the volume defined by the surface.

 

What is CURRENT and what is VOLTAGE ?

VOLTAGE 
 

Every atom has its own complement of electrons. In a conductor, some of those electrons can jump from atom to atom. But electrons don't move from atom to atom without a reason. When electrons are flowing there is always an electrical force pushing them along. We refer to this force as "Voltage". 

Voltage, also called electromotive force, is the potential difference in "charge" between two points in an electrical field. In other words, voltage is the "energy per unit charge”. 

We define voltage as the amount of potential energy between two points on a circuit. One point has more charge than another. This difference in charge between the two points is called voltage. It is measured in volts, which, technically, is the potential energy difference between two points that will impart one joule of energy per coulomb of charge that passes through it (don’t panic if this makes no sense, all will be explained). The unit “volt” is named after the Italian physicist Alessandro Volta who invented what is considered the first chemical battery. Voltage is represented in equations and schematics by the letter “V”.

CURRENT

Current is the rate at which electric charge flows past a point in a circuit. In other words, current is the rate of flow of electric charge.

This picture illustrates a single cell pocket flashlight. The 1.5 Volt cell is pushing the electrons through the bulb and the wire. Without this push, the electrons would be happy to remain stationary. In this case, chemical action within the battery causes the push. When the battery gets old, its chemical reaction slows down and its internal push gets weaker and weaker. (That's why the bulb gets dim.) http://www.reprise.com/host/electricity/voltage.asp

Who Does the Work?

Current, not Voltage, does the work in electrical circuits. The flow of water through a turbine is what makes the turbine spin. The flow of current through an electrical circuit is what lights the bulb, heats the stove, runs the motor, etc. Routing and controlling the flow of current is the goal of every electrical circuit. 


A detailed comparison between current and voltage as on Diffen.com:

	Current	Voltage
Definition	Current is the rate at which electric charge flows past a point in a circuit. In other words, current is the rate of flow of electric charge.	Voltage, also called electromotive force, is the potential difference in charge between two points in an electrical field. In other words, voltage is the "energy per unit charge”.
Symbol	I	V
Unit	A or amps or ampere	V or volts or voltage
SI Unit	1 ampere =1 coulomb/second.	1 volt = 1 joule/coulomb.
Measuring Instrument	Ammeter	Voltmeter
Relationship	Current is the effect (voltage being the cause). Current cannot flow without Voltage.	Voltage is the cause and current is its effect. Voltage can exist without current.
Field created	A magnetic field	An electrostatic field
In series connection	Current is the same through all components connected in series.	Voltage gets distributed over components connected in series.
In a parallel connection	Current gets distributed over components connected in parallel.	Voltages are the same across all components connected in parallel.