Topic 4 - Electronics

Question 1

What is electricity?

Answer 1

The movement or build-up of charged particles

Question 2

What is static electricity?

Answer 2

The accumulation of charged particles

Question 3

What is electric current?

Answer 3

The flow of charged particles, typically electrons / ions, through a conductor

Question 4

Conventional current

Answer 4

• 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

Question 5

Electron flow

Answer 5

• 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

Question 6

Direct current (DC)

Answer 6

• 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

Question 7

DC - Drift velocity

Answer 7

• 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

Question 8

Alternating current (AC)

Answer 8

• 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

Question 9

AC

Answer 9

-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

Question 10

AC power transmission

Answer 10

• 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

Question 11

Electric charge

Answer 11

• measured in coulombs (C)
• 1 Coulomb = 6.24150934×1018 electrons

Question 12

Electric current:

Answer 12

• flow of electric charge
• charge is carried by electrons moving in a wire
• measured in coulombs per second (C/s) = Amps / Amperes (A)

Question 13

Voltage

Answer 13

• 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)

Question 14

Basic circuit

Answer 14

• 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

Question 16

Ohm’s Law

Answer 16

V = IR
- v: potential difference, volts (V) - driving force
- I: current, amps (A) - flow of charge
- R: electrical resistance (ohms) - resistance

Question 17

Electrical power

Answer 17

P = IV
- P: power (Watts , J/s)
- V: voltage (volts, J/C)
- I: current (amps, C/s)

Question 18

Electric components

Answer 18

• Building blocks used to create electronic circuits

Question 19

Resistors

Answer 19

• restrict flow of electrons in a circuit
• provides a precise amount of resistance
• fundamental to controlling voltage and current within a circuit

Question 20

Capacitors

Answer 20

• store electrical energy temporarily
• influence the rate of which voltage builds up and drops within the circuit
• crucial in timing and filtering applications

Question 21

Inductors

Answer 21

• oppose changes in current flow
• store energy in a magnetic field when a current flows through them
• useful in filtering and tuning circuits

Question 22

Diodes

Answer 22

• 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

Question 23

Transistors

Answer 23

• 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

Question 24

integrated circuits (ICs)

Answer 24

• 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

Question 25

Central Processing Units - CPUs

Answer 25

• use thousands of transistors in sophisticated architectures, enabling complex calculations
• heart of any computing device, implementing software instructions and managing data flow

Question 26

Passive components

Answer 26

• 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

Question 27

active components

Answer 27

• 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

Question 28

Resistors

Answer 28

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.

Question 29

Resistors in circuits

Answer 29

𝑅_𝑇=𝑅_1+𝑅_2+𝑅_3
where 𝑅_𝑇 is the total resistance in the circuit

Question 30

Resistors in parallel

Answer 30

𝑅_𝑇=1/(1/𝑅_1 +1/𝑅_2 +1/𝑅_3 )

Question 31

Resistivity

Answer 31

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)

Question 32

Area of a round wire

Answer 32

A = pi x d^2 / 4
A is area, m^2
d is diameter, m

Question 33

Transistors

Answer 33

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

Question 34

Semiconductors

Answer 34

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.

Question 35

p-type silicon

Answer 35

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

Question 36

n-type silicon

Answer 36

n-type silicon is
doped with a Group-V element (circa 1 ppm)
n-type conduction via movement of free electrons

Question 37

Field Effect Transistor (FET)

Answer 37

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”