Electrons

Motivation

• Most hardware involved in the IoT uses electrical energy to work.

  The structure of an atom

• All elements are made up of atoms.

• Atoms have a nucleus which contains positively charged protons and neutrally charged neutrons, usually the same amount of each.

• Orbiting around the nucleus are negatively charged electrons forming a cloud that occupies a volume 10000 times larger than the nucleus.

  How the electricity occurs

  

• Materials can accumulate and lose electrons.

• A material that has accmulated an excess of electrons is described as negatively charged.
• On the other hand, when a matrial has a deficit of electrons, it is described as positively charged.
• Another word used to describle the state of charge is electrical potential.
• Things in nature tend to a state of equilibrium; hence electorns will flow wherever there is a difference in charge between two points.
• So electricity occurs when electrons in atoms jump from one atom to another
• The number of electrons flowing depends on the difference of charge between two points
• The unit for electric charge is the Coulomb.
  • One Coulomb is equal to the electric charge of 6.24 X 1018, or 6.24 quintillion electrons

• It is worth noting that although electrons physically move from a negatively charged point to a positively charged one, it is conventionally accepted that for the purpose of analysis and design, electric current flows from a positively charged to a negatively charged point.

  Where does electricity come from?

• The flow of electrons, can be produced in many ways.

• However, since enery cannot be created or destroyed, only transformed, to produce electric enery weneed to first inject other forms of energy. Sometimes we burn fossil fuels and other non-renuewable resources to produce steam which, properly channelled, moves the rotating part of a generator. Sometimes we use solar and other renewable resources to produce electricity.

  Current, voltage, resistance

  Electric current

• The flow of electrons jumpin between atoms from a negatively charged to a positively charged point is called electric current(I).

• Electrical current is measured in Amperes.

• One Ampere represents the flow of one Coulomb of charge per second.

  Vlotage

• The difference in electric charge between two points is called voltage(V).

• The greater the charge difference(voltage) between two points, the higher the electrical current that will flow.

• The unit for voltage is the Volt.

  Resistance

• Since all materials are made out of atoms, all of them have electrical properties.

• One important property is the ability called resistance(R) to conduct electricity.
• Good electrical conductors have low resistance, while materials that are not very good at conducting electric currents have high resistance.

• The unit for resistance is the Ohm(Ω)

  Resistors

• In electrical circuits, resistance is often provided by resistors.

• Common symbols for resistors

Ohm’s law

There is a very important relationship between voltage, current and resistance.

• One Volt can push a current of one Ampere through a resistance of one Ohm.
• That means the current flow through a conductor is directly proportional to the potiential difference(voltage) and inversely proportional to the resistance.
• _I = V/R, _Where electric current(I) eqals voltage(V) divided by resistance(R)

• The defferent expressions of Ohm’s law

Ohm’s wheel and electric power

• Power(P) is the rate at which energy is transferred or transformed over time;
• Power is measured in Joules per second or Watts.

• Electric power is the product of voltage and current, or: P = V*I

• Where power(P) equals voltage(V) multiplied by electrical current(I).

• The wheel shows 12 formulas three for each component - power, voltage, resistance and current

Capacitors and Inductors

Capacitors

• These devices have the ability to store energy as electric charge.
• You may think of capacitors as tiny batteries than can be charged and discharged very quickly.
• Capacitors are useful to smoothen analogue signals and to decouple power hungry devices from the power supply.
• The ability to store charge is called capacitance.
• The unit of capacitance is the farad.
• however one farad is too big and commercial capacitors are measured in micro (10 ) or nano (10 ) farads.

Inductors

• These devices have the ability to store energy as magnetic fields when an electric current flows through them.
• Physically inductors are long wires wound into a coil around a core.
• The unit of inductance is the henry

• But like capacitors one henry is too big and commercial inductors are rated in milli (10 ) or micro (10 ) henrys.

  Semiconductors

  

• In some materials, electrons are free to move and they are called conductor. Most metals are very good conductors.

• In other materials, electorns are not free to move and they are called insulators. Rubber and glass are examples of good insulators.
• Other materials are neither good conductors nor insulators; they are called semiconductors. You may think of semiconductors as materials that need a little help to become good conductors.
• At an atomic level, insulators require enormous amounts of external energy for electrons to move long distances; while in conductors a difference in charge between two points is enough to get electrons moving.
• Under everyday conditions, conductors cannot turn into isulators, and vice-versa.
• With semiconductors, we need to apply a bit of external energy to get those electrons moving, turning the material into a conductor. But as soon as the external energy source is removed, the material goes back to its insulating state.
• The most common materials that present semiconductor properties are Silicon(Si) and Germanium(Ge).
• To make semiconductors useful - that is, to make it easy to control the amount of current flowing through them - they have to be ‘contaminated’ with other materials. These foreign ingredients are called dopants.
• Dopants are added to Silicon and Germanium to either increase or decrease the number of free electrons inside them.
  • If dopants give the material an excess of electorns, then it is called negative(N-type) semiconductor.
  • If dopants produce a deficit of electrons, then the material is called a positive(P-type) semiconductor.
• Examples of common dopants are Phosphorus for N-type, and Boron For P-type semiconductors.

Diodes

• A diode is a 2-terminal device that is very good at conducting electricity in one direction only.
• It is made with one part N-type and one part P-typ semiconductors.
• Its two terminals are called anode and cathode.
• Diodes become good conductors when the anode becomes more positive than the cathode by means of an external voltage supply.
• Structure and common symbols for diodes.

• Diodes are commonly used as signal rectifiers or voltage references.

  Transistors

  Bipolar Junction Transistor (BJT)

• A Bipolar Junction Transistor is a 3-terminal device whose level of conductivity can be controlled with a small amount of current.

• It is made with three layers of semiconductor: N-P-N, or P-N-P. It’s terminals are called: Base, Collector and Emitter.

• Bipolar junction Transistors can be modelled with two diodes as shown in the following figures:

Field Effect Transistor(FET)

• Like BJTs, Field Effect Transistors are 3-terminal devices whose conductivity can be controlled with an external small voltage.
• The three terminals are called: Gate, Source and Drain.

• Field Effect Transistors are very important because most of today’s electronic devices use them as their main building block.
• When FETs are in saturation or cut-off state, they consume practically no power because no current flows through them.
• Power consumption only occurs during transistions between the saturation and cut-off states.