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Samenvatting vak 'Electricity, Electronics and Photonics'

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Vrije Universiteit Brussel (VUB)

In dit document vind je een samenvatting terug van het vak 'Electricity, Electronics and Photonics'. Dit vak werd door Prof. Schretter C. gedoceerd.

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Publié le 27 septembre 2024
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Écrit en 2023/2024
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Electricity and electronics
ELECTRICITY
From electrons to light

Needed for the flow of the electrons

Needed for grounding (security mechanism)

Electron flow in copper wire
The model is an illustration of how electrons are moving during the process
-> !important to know!
never an electron goes lost during the process, otherwise we have a short circuit
possible reason of loss electrons: - default in the circuit
- someone is being electrocuted
-> the grounding has the task to detect a leak and stopping the process (security mechanism)

- Electrons always goes from – to +
- Flow of electric current in opposite direction
- No electron goes lost during the process

when no power/battery linked to the wire, electrons
are moving freely and in random directions (less fast
than with a battery because of kamertemperatuur)
-> is de reden wrm een metaal een goede geleider is,
door de vrij bewegende elektronen

Which metal is the best conductor?
The reason why a metal is a possible good conductor is because of ‘de vrije valentie elektroon’ on the
last shelf of the atom. Is easy to take him away of the atom
-> when you put a battery, the battery makes the electrons move in different directions
when electron A goes away from its molecule, electron B can easily take the place of electron A

In the past: we used very noble metals, like silver and copper
nowadays: everything between conductor and isolator like Germanium ex. In chips (less quality but
works also good enough)
-> need to look at the resistivity of a metal

How easy an atom will move (how strongly
does the material resists to electric current)
-> expressed in ‘Ohms’

,Reasons for resistance: friction (creation of heat)
possible solution: have a thicket wire/filament
-> more capacity because bigger diameter
-> less friction for the electrons
-> less creation of heat
-> less energy consumed

!Important to know!

Resistivity is dependent on temperature

When 2500 °C, a steady points is reached
(resistivity will not change anymore)

When the temperature is that low that there is no resistivity, we have superconductivity.

The drift speed of electrons
‘the smaller the wire, the faster the electrons need to move’

The transmission speed of electrons
Electrons push against each other

How to remember the basics of electric power?
-> can compare it with ‘la pêche aux canards’
a pump is creating the flow of the water
- there is no leak (no drop of water is getting lost)
- is a continuous loop (geen onderbrekingen)
- it goes very slow

Basic formulas that we will use

,The war of currents
There are 2 types of currents: DC (direct current) and AC (alternate current)

Direct current
created by Thomas Edison
before the creation of electro-mechanical generators, we could only create electricity thanks to piles
-> was the first form of public lightening

You see there the army of piles needed to
make one big lightbulb lightening up
-> the light was very bright
(first form of public lightening)

HOW DOES IT WORK?
In a carbon arc lamp, the electrodes are carbon rods (= koolstaafjes) in
free air. To ignite the lamp, the rods are touched together, thus allowing a
relatively low voltage to strike the arc. The rods are then slowly drawn apart (op
die manier wordt plasma gecreëerd), and electric current heats and maintains an
arc across the gap. During the jump of the electrons, friction is happening, this
creates heath and when the heath is high enough we can see photons.

After that, Zénobe Gramme invented an efficient dynamo machine
This is a machine that is able to produce a very smooth
continuous direct current at high voltage
HOW DOES IT WORK?
it transforms mechanical energy into electrical energy

Problem
lot of friction is created
-> need to have very short distances and lowest resistance
possible

Alternate current

Tesla invented a new system, namely the alternate current
HOW DOES IT WORK?
you have a rotating disk with on it a multitude electromagnets -> moves against a cable
when the disc is moving tegenwijzerzin, magnets will attract the electrons present in the
cable and then push them back (reason why you have an alternate current)

pull

push

, !important to know!

In reality, the amplitude is not always exactly equal (the
amplitude move a bit, but not too much)
same goes for direct current, it is not exactly a constant

 AC always has a moment where they are not in motion while DC is always in motion.

Practical – direct current
Power is the product of current intensity and voltage difference -> P = V*I
= difference of potential electromotive forces

!important to know!

When current is equal to 0, the lightbulb will not lighten up

When there is no resistance you get infinte flow and it will explode -> short circuit
Voltage drop is the force consumed by the resistance.

Terminology

 I = intensity (of the electric current)
-> is the rate of the flow of positively charged particles in the circuit
-> A (Amperes)

 V = tension/potential (the electric voltage)
-> provides the ‘push’ for the flow of positively charged particles
-> V (Volts)

 R = resistance (of a circuit)
-> measure of its opposition to the electric current
-> Ω (Ohms)

 P = electric power
-> rate, per unit time, at which electric energy is transferred by an electric circuit
-> W (Watts)

!important to know!

Battery = push
resistance = pull
the current in a system is always the same, but the voltage can differ

Exercices (see notes from class and slides)

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