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Samenvatting - Electricity Electronics and Photonics
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This document contains all the theory and detailed exercises for the EEP open book exam.
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PART 1: ELECTRICITYPHYSICS OF ELECTRON FLOW
Industrial age: use of electrons for transmission of power (electrons => photons)
working of a light bulb: a battery pushes electrons thanks to a chemical reaction inside the pile. The electrons move from the negative
terminal of the battery to the positive terminal. When the electrons flow through a filament with high resistance, they colli de with the
atoms of the filament material, creating friction, creating heat, (heating up to about half the surface temperature of the sun) T of f ilament
high enough to emit visible light. The filament is very thin for increasing the resistance. If we double the length of a filament, the
resistance will double (idem effect as making it thinner)(prop to length)(lightbulb will consume less), the current will halve (V=IR)
(same amount of voltage)(idem principe as parallel) and the light intensity (proportional to power) will decrease by a factor 2.
(P=V^2/R)
(cutting a filament = infinite resistance )
working of a cable: consists out of wires with an overall cable jacket → mechanical protection, wire insulation → electrical isolation
(separating conductors, preventing short circuits and interference between them), stripped wire → conductivity (allows transmission of
electrical signals or power through the cable)
cascade effect = the flow of electrons in a material triggers a sequential transfer of additional electrons, resulting in an amplification of
the initial current.
Electromagnetic induction: production of electric current or voltage in a conductor when exposed to a changing magnetic field -
Faraday’s law of electromagnetic induction
Electric current: the flow of electric charge in a conductor through a closed circuit, caused by a potential difference.
Resistance (measured in Ohm) depends on the resistivity of the material, the length of the wire and the temperature.
Drift speed of electrons (drift velocity): u = I/ (nAq) with A the cross-section area (thick wire <-> thin wire)
<-> signal velocity: the speed at which a signal/information transfers into a medium. It represents how quickly a change/disturbance can
propagate from one point to another.
I (electric current intensity): the rate of the flow of positively charged particles in the circuit (A)
V (electric voltage, potential difference): provides the “push” for the flow of positively charged particles (V)
R (electric resistance of a circuit): is a measure of its opposition to the electric current (Ohms)
= amount of friction, higher when you reduce the cross section of the wire (thin wire)
P (electric power): rate at which electric energy is transferred by an electric circuit (W)
Charge: represents the electrons and the flow (in Coulomb)
R = V2/P
V=IR (Ohms law)
P=VI: Knowing only the voltage of a power supply won’t tell you anything about the total amount of energy that it can supply. You
need Intensity and time! Work = Energy = Power x time (In Joules)
DC (Graph): electrical current that flows in one direction, form a positive terminal to a negative terminal. The magnitude and direction
of the current remain constant over time. (Application: Dynamo machine, used in specific electronic applications; batteries etc)
AC: periodically changes its direction. The current alternates its polarity, generated by generators. (Used for power distribution over long
distances in homes and cities)
Application: electric arc lamp: rotating wheel (driven by water) with a magnet on it. Projected motion follows a sinusoid. The magnet
will attract electrons. The magnet and therefore the electrons will be pushed and pulled.
→ as the waveform oscillates, it reaches points where the current value is zero.
Plasma: fourth state of matter. Formed when a gas is heated to extremely high temperatures, causing atoms to lose or gain electrons and
become ionized. This process creates a conductive medium capable of carrying electrical currents.
Analogy with hydraulic power: When a pipe is clogged with hair, it takes more pressure to achieve the same flow of water = using a
higher voltage (electromotive force) on a thin wire for the same amount of electricity (current).
Devices: I → Ammeter; V → Voltmeter, put before and after the resistance and measures the difference of potential force before and
after the resistance
ELECTRIC CIRCUITS (3 elements)
Resistors: are used to control the amount of current or voltage in a circuit by providing resistance. (In Ohms)
Capacitors (batteries): store electrical energy in an electric field. They consist of 2 conductive plates separated by dielectric material (in
Farads)
Inductors: store electrical energy in a magnetic field. They are made of a coil of wire and are used to store and release energy in a
circuit. (in Henrys)
Open circuit: disconnected wire or component failure → break in the path of the current flow; no transfer of electrical energy
Conductance 1/R: measure of how easily an electrical current can flow through a material or a component → resistance
Nodes: points in a circuit where 2 or more branches connect. At a node de electrical current splits and combines as it flows through the
connected components.
Branches: individual paths between 2 nodes.
Loops: a closed path in a circuit that starts and ends at the same node, without passing through any other node more than once.
2 important properties of circuits:
Kirchhoff’s Current law: the current flow of electric charges never leaves. The current intensity entering a junction is equal to the current
leaving that junction.
Kirchhoff’s Voltage law: the voltage differences along a loop cancel out. All potential differences around a loop sum up to zero.
Functioning of capacitors: You have one plate with an insulation medium and then another plate. You have an electric current that
wants to pass from one plate to the other but since the insulation medium is dielectric it can’t pass. The blue arrows repres ent the flow
current (in reality that arrow would go in the opposite direction).
The storage capacity will depend on the charge that is on the plate and the force that’s sticking to that plate.
→ The larger the charge Q, the more energy you can store.
→ The larger the area of the plate, the more charge you can put on the plate
, The electric capacitance is the ration of the change in electric charge of a system, to the corresponding change in its electric potential.
Measured in Farads (F).
When we use capacitors, we always use them with a certain time dimension. You want to accumulate the charges on the plate and then
you want to discharge it (to get the energy). It’s an element that will react when then intensity of the current is variable, not in DC mode
but in variable current mode.
Charge and discharge: there’s an accumulation of electrons until the maximum capacity and then you have a discharge when you apply
the differential potential.
Relation I & V: (Graph)
→ RC circuits: at maximum charge (voltage), you have a peak in current and it is discharging very quickly.
→ AC Resistor: follows the current flow. When there’s zero voltage, you have no current and there’s no flow of electrons. The more
voltage, the more current.
→ AC Capacitor: Capacitors damp the current flow in AC circuits. As the voltage across the capacitor changes, the capacitor alternately
stores and releases charge. This charging and discharging causes a lag or delay in the current flow. It causes the current to be out of phase
with the voltage, resulting in a decrease in the intensity of the current.
Modern design: design of the anode. It uses nanotechnology materials to optimize the packing of the charge. Instead of the electrons
roaming around on the metal plate, they are now ordered. This allows you to put a lot more charge on the plates and increase the density
of storage.
Lithium-ion batteries: Consists of a positive (cathode) and negative electrode (anode). During charging, lithium ions move from the
cathode to the anode through the electrolyte, creating a flow of electrons. This process is reversable allowing the battery to be charged
and discharged (the lithium ions move from the anode back to the cathode.
Dynamite: fast withdraw of energy.
Hydroelectricity: The water will be pumped up to the upper reservoir and during the peak hours they release the water down. The water
will go through the tube at high speed and once it goes through the generator it’ll generate power.
PART 2: ELECTRONICS
Electronics: comprises the physics and engineering that deal with the flow of electrons in vacuum, gas and semiconductors.
Electrical engineering: uses passive components (such as resistors, capacitors and inductors)
Electronic engineering: uses active devices (such as transistors) to control the electron flow by amplification and rectification.
Active components: have the ability to control, amplify or generate electric signals. They can introduce gain or power into the circuit.
→ Battery: uses chemical reactions to create electricity.
→ Generator: this burns gas and converts it to create electricity
→ Transistors: These can be used to control a source of current by passing a small flow between the pins. So it won’t create electricity
but it will control the power source that is connected to it.
Passive components: do not introduce gain or power to the circuit. They can only store, dissipate or react to electrical energy.
→ Capacitors: non-conductive material and symmetrical, positive charges accumulate on the anode and the negative charges on the
cathode.
→ Resistors: also symmetrical but use conductive material between the plates
→ Diodes: A diode is different from a resistor or capacitor because it has an orientation, a direction, that is represented by the tria ngle in
the picture above. And it uses semi-conductive materials. If the current passes from the left to the right, it’ll let the electrons pass (in this
case). However when the current flow is switched (right to left), the diode will block the electrons. There’s zero resistance in one
direction and infinite resistance in the reverse direction.
→ Capacitors: use non-conductive materials (positive charges accumulate on the surface) and the direction of current flow doesn’t
matter
→ Resistors: use conductive materials (but resistant) and direction of the flow doesn’t matter.
Functioning of diodes: diodes use a semi-conductive material. That material will be doped (p- doped or n-doped). In a negatively doped
region, the material structure is slightly modified to get a majority of free electrons. (adding atoms with extra valence electrons =>
creates more conductivity) In a positively doped region, you have a majority of holes. (adding atoms with less valence electrons =>
creates holes and less conductivity). The junction of those two region is called the depletion zone. In that area, the electrons will fill the
holes. However, this will only happen if the current flow is coming from the right direction. If the current is coming from the opposite
direction, the material will act as an insulator and will create a blockage barrier. So in conclusion, if the current is in t he right direction,
you get a short circuit. Otherwise you’ll get an open circuit.
Non-linear circuit element: Graph The red line represents the perfect ‘switch’. Once the voltage passes zero, the diode immediately
forms a blockage. However, in reality the ‘on switch’ will not happen so suddenly. The depletion region will change smoothly and
exponentially (represented by the blue line). After a while this exponential growth will change to a linear one due to saturation.
Real current flow intensity: Graph depending on voltage tension. The other imperfection in real life is that the current will go through
after a while. If you apply a negative voltage that’s high enough, the resisting force (aka blockage) won’t be high enough to counter it.
This is represented by the avalanche region.
Transistors: A transistor is a three-terminal electronic component that amplifies or switches electrical signals. It’s an active dependent
source of current. A transistor doesn’t really have a cathode/anode rather, it has a collector, a base and an emitter.
The electrons can take a lot of different paths. Some electrons will flow to the base and others will pass through it and go t o the collector.
Dependent switches: Output current is directly influenced by the input current/voltage applied. The (small) current between the emitter
and the bass controls the conductive power between the emitter and the collector. So the conductivity of the transistor depends on the
current between the emitter and the base. By controlling the current or voltage applied to the base terminal, the transistor can be turned
on or off.
Another way to look at it is that the current between the base and the emitter carries information and once the larger flow p asses the base,
its current intensity will be multiplied depending on that information. So a transistor allows you to amplify the current.
Functioning of transistors: consists of 3 layers of semiconductor material: emitter, base and collector. These layers are N-type or P-
type. Transistor operates based on biasing and junction behavior:
→ Biasing: Forward: provides the necessary voltage to overcome the junction barrier and allow current flow while reverse biasing
blocks current flow.
→ Junction: base-emitter junction and base-collector junction (depletion zones where electrons fill the holes)
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