Topic 4 - Electronics Flashcards
What is electricity?
The movement or build-up of charged particles
What is static electricity?
The accumulation of charged particles
What is electric current?
The flow of charged particles, typically electrons / ions, through a conductor
Conventional current
- flow of positive charge
- flow is from the positive terminal of a power source to the negative
- the direction was established in the early days of electrical theory by scientists who believed that electrical current flowed in this manner
Electron flow
- actual movement of electrons in a circuit
- flow from the negative terminal to positive of a power source
- electrons are negatively charged, movement constitutes the real flow of charge in most circuits
Direct current (DC)
- type of electrical current that flows in one constant direction
- produced by batteries and solar panels
- provides a constant voltage, used to power portable devices and electric vehicles
DC - Drift velocity
- average speed at which free electrons move through a conductor
- electrons drift slowly, electric signal propagates at a significant fraction of the speed of light
- typical drift velocities are in the order of m/s
Alternating current (AC)
- type of electric current where the direction of flow reverses periodically
- the electric grid and transmits alternating current to homes and businesses
- used to power appliances, lightning and machinery
AC
-has a frequency, pertains to how many times the current changes direction per second
- generated by rotating a coil within a magnetic field or vice versa, creates a sinusoidal voltage and current waveform
- frequency depends on the rotational speed of the generator
AC power transmission
- ac power is more suitable for long-distance electricity transmission, can easily be transformed to higher / lower voltages using transformers: helps reduce energy losses
- transformers use electromagnetic induction to transfer electrical energy between wire coils
- AC can also be converted to DC when required
Electric charge
- measured in coulombs (C)
- 1 Coulomb = 6.24150934×1018 electrons
Electric current:
- flow of electric charge
- charge is carried by electrons moving in a wire
- measured in coulombs per second (C/s) = Amps / Amperes (A)
Voltage
- potential difference between two points
- moving 1C of charge across 1 volt of p.d requires 1 joule of work
- measured in joules per coulombs (J/C) = (V)
Basic circuit
- power supply: pushes charge around circuit
- voltmeter: measures p.d in volts (j/c)
- resistor: resists flow of charge
- ammeter: measures flow of current in amperes ( C/s)
- difference pressure cell: makes pressure drop
- pump: pushes liquid around circuit
- long/narrow pump: resists flow of liquid
- flow meter: measures flow of liquid
Ohm’s Law
V = IR
- v: potential difference, volts (V) - driving force
- I: current, amps (A) - flow of charge
- R: electrical resistance (ohms) - resistance
Electrical power
P = IV
- P: power (Watts , J/s)
- V: voltage (volts, J/C)
- I: current (amps, C/s)
Electric components
- Building blocks used to create electronic circuits
Resistors
- restrict flow of electrons in a circuit
- provides a precise amount of resistance
- fundamental to controlling voltage and current within a circuit
Capacitors
- store electrical energy temporarily
- influence the rate of which voltage builds up and drops within the circuit
- crucial in timing and filtering applications
Inductors
- oppose changes in current flow
- store energy in a magnetic field when a current flows through them
- useful in filtering and tuning circuits
Diodes
- only allow current to flow in one direction
- use p-type and n-type semiconducting materials to create a p-n junction
- junction acts as an insulator until sufficient voltage with the correct polarity is applied
Transistors
- can switch or amplify electrical signals
- use p-type and n-type semiconducting materials
- referred to as “solid-state” because they have no moving parts
integrated circuits (ICs)
- compact devices that contain tiny electric components embedded within a single semiconductor chip
- perform a variety of electronic functions, including amplification, signal processing and calculations
Central Processing Units - CPUs
- use thousands of transistors in sophisticated architectures, enabling complex calculations
- heart of any computing device, implementing software instructions and managing data flow
Passive components
- do not have a power gain
- cannot amplify/generate energy
- store energy temporarily (capacitors and inductors) or dissipate it as heat (resistors)
- don’t require an external power supply
- function is solely based on their physical properties and the role they play within the circuit’s voltage and current characteristics
active components
- have a power gain
- introduce extra power into a circuit
- output more power than they receive from the input signal
- require an external power supply:
- They use this power to perform tasks such as amplifying signals
Resistors
Resistors restrict the flow of electrons in a circuit.
The level of resistance is measured in ohms (Ω).
Many resistors have colour bands to indicate their resistance.
Resistors in circuits
𝑅_𝑇=𝑅_1+𝑅_2+𝑅_3
where 𝑅_𝑇 is the total resistance in the circuit
Resistors in parallel
𝑅_𝑇=1/(1/𝑅_1 +1/𝑅_2 +1/𝑅_3 )
Resistivity
𝑅=𝜌𝐿/𝐴
R is electrical resistance (ohms or Ω)
L is length of material (m)
A is the cross-sectional area of material (m²)
ρ is resistivity of the material (Ω m)
Area of a round wire
A = pi x d^2 / 4
A is area, m^2
d is diameter, m
Transistors
Transistors can switch or amplify electrical signals.
They use p-type and n-type semiconducting materials.
Transistors are referred to as “solid-state” because they have no moving parts
Semiconductors
Semiconductors have an intermediate electrical conductivity.
Typically, 1 to 100Ωm (between that of an insulator and a conductor).
Semiconductor materials used in transistors include p-type silicon and n-type silicon.
p-type silicon
p-type silicon is
doped with a Group-III element (circa 1 ppm)
p-type conduction via migration of positive “holes” arising from a “missing” electron
n-type silicon
n-type silicon is
doped with a Group-V element (circa 1 ppm)
n-type conduction via movement of free electrons
Field Effect Transistor (FET)
FET consists of:
- “source” where charge enters the transistor
- “channel” through which the charge can flow
- “drain” where charge exits the transistor
- Current flowing through FET is influenced by the voltage applied to the “gate”
