Basics

Question 1

What is the loose generalised distinction between the terms ‘electrical’ and ‘electronic’?

Answer 1

Loosely speaking, both terms relate to the use of electrical energy, but the two terms can be used slightly differently in different disciplines and in different countries.

Within reason, we can say:

Electrical - often used to refer to applications concerned with the generation, transmission or use of large amounts of electrical energy.

Electronic - used for applications involving smaller amounts of power. In many cases, the electrical energy is used to convey information rather than as a source of power.

Question 2

What is the Systems Approach?

Answer 2

The Systems Approach combines the Systematic approach (breaking a complex problem into to smaller and smaller easily understood sub-systems) with an understanding of S**ystemic issues (chatacteristics that are features of the system as a whole).

A key feature being that it places as much importance on the relationships between components, as it does on the components themselves.

Question 3

In electrical/electronics what is meant by the word system?

Answer 3

In an engineering context, a system can be defined as a closed volume for which the inputs and outputs are known. This concept is very flexible in its applications, but the term is notmally reserved for arrangments that perform some useful function.

Question 4

What aspects of electrical and electronic systems fall within the realm of generation?

Answer 4

Electrical

(usually production of electricity for use as a power source)

• Electrical generators in power stations or hydroelectric dams etc.
• Smaller units such as altenators in cars etc.

Electronic

(usually production of electrical signals used to represent physical quantities, rather than as source of power)

• Sensors that produce electrical signals in response to changes in their environment. e.g. photodiode.

Question 5

What aspects of electrical and electronic systems fall within the realm of Transmission?

Answer 5

Electrical

(often concerned with the distribution of electrical power)

• Overhead or underground cables.
• Thick copper wires in smaller applications.

Electronic

(more often concerned with the transmission of information)

• Electrical wires or optical cables.
• Alternatively, radiowaves or microwaves.

Question 6

What aspects of electrical and electronic systems fall within the realm of control or processing?

Answer 6

Control is related to command and regulation functions. Varies from the simplest form of control, a switch, to far more complex forms of control.

Electrical

• regulation or variance of power supplied to certain apparatus.

Electronic

• performance of complex processing functions, perhaps using computer based techniques.

Question 7

What aspects of electrical and electronic systems fall within the realm of utilisation?

Answer 7

Utilisation is concerned with the use of electrical energy to perfom some useful function. Widely varied set of elements that produce the required output of a system.

Electrical

• production of heat, light or motion.

Electronic

• production of sound or the display of visual information

Question 8

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Capacitance?

Pay attention to capitalisation and italicisation.

Answer 8

Quantity - Capacitance

Quantity Symbol - C

Unit - farad

Unit Symbol - F

Question 9

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Charge?

Pay attention to capitalisation and italicisation.

Answer 9

Quantity - Charge

Quantity Symbol - Q

Unit - coulomb

Unit Symbol - C

Question 10

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Current?

Pay attention to capitalisation and italicisation.

Answer 10

Quantity - Charge

Quantity Symbol - I

Unit - ampere

Unit Symbol - A

Question 11

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Electromotive Force?

Pay attention to capitalisation and italicisation.

Answer 11

Quantity - Electromotive Force

Quantity Symbol - E

Unit - volt

Unit Symbol - V

Question 12

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Frequency?

Pay attention to capitalisation and italicisation.

Answer 12

Quantity - Frequency

Quantity Symbol - f

Unit - hertz

Unit Symbol - Hz

Question 13

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Inductance (self)?

Pay attention to capitalisation and italicisation.

Answer 13

Quantity - Inductance (self)

Quantity Symbol - L

Unit - henry

Unit Symbol - H

Question 14

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Period?

Pay attention to capitalisation and italicisation.

Answer 14

Quantity - Period

Quantity Symbol - T

Unit - second

Unit Symbol - s

Question 15

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Potential Difference?

Pay attention to capitalisation and italicisation.

Answer 15

Quantity - Potential Difference

Quantity Symbol - V

Unit - volt

Unit Symbol - V

Question 16

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Power?

Pay attention to capitalisation and italicisation.

Answer 16

Quantity - Power

Quantity Symbol - P

Unit - watt

Unit Symbol - W

Question 17

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Resistance?

Pay attention to capitalisation and italicisation.

Answer 17

Quantity - Resistance

Quantity Symbol - R

Unit - ohm

Unit Symbol - Ω

Question 18

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Temperature?

Pay attention to capitalisation and italicisation.

Answer 18

Quantity - Temperature

Quantity Symbol - T

Unit - kelvin

Unit Symbol - K

Question 19

What is the Quantity Symbol, the SI Unit and the Unit Symbol for Time?

Pay attention to capitalisation and italicisation.

Answer 19

Quantity - Time

Quantity Symbol - t

Unit - second

Unit Symbol - s

Question 20

Briefly discuss electric current.

Answer 20

An electric current is a flow of electric charge (in most cases the flow of electrons). Conventional current is defined as a flow of electricity from a positive to a negative region. This is opposite to the flow of negatively charged electrons.

The unit of current is the ampere or amp (A)

A sustained electric current requires a complete circuit for the recirculation of electrons. It also requires some stimulus to cause the electrons to flow around this circuit.

Question 21

What aspects of electrical and electronic systems fall within the realm of storage?

Answer 21

The storage of electrical energy occurs in both areas, but electronic is usually more concerned with storing information.

Electrical

• electrical energy can be stored directly, as in a capacitor, but this is usually achieved by converting into another form (e.g. GPE in flywheels or raised reservoirs, chemical as in rechargeable betteeries).

Electronic

• can be small scale energy storage.
• more commonly information, as in the case of random-access memory (RAM).

Question 22

Discuss electromotive force (e.m.f.) and potential difference.

(sorry, not brief)

Answer 22

electromotive force (e.m.f.) is the stimulus that causes an electric current (electrons) to flow around a circuit. The e.m.f. represents the energy introduced to a circuit by a source (e.g. battery or generator).

The energy transferred from the source to the load results in a change in the electrical potential at each point in the load. Between any two points in the load there will exist a certain potential difference, which represents the energy associated with the passage of a unit of charge from one point to the other.

Both e.m.f. and potential difference are expressed in units of volts, which highlights that the two quantities are related. Figure below illustrates: e.m.f. is the quantity that produces an electric current, while potential difference is the effect on te circuit of this passage of energy.

Question 23

Briefly discuss voltage reference points.

hint: it’s beneath you.

Answer 23

Electromotive forces and potential differences in circuits produce different potentials (voltages) at different points in the circuit. It is normal to describe the voltages throughout a circuit by giving the potential at a particular point with respect to a single reference point.

This reference point is often called the ground or earth of the circuit. The voltage on the ground itself is zero, therefore the ground is also called the zero volt line.

Question 24

Briefly discuss Direct Current (DC).

Answer 24

Direct Current (DC) is defined as the unidirectional flow of current.

Voltage and current can vary over time so long as the direction of flow does not change.

Question 25

Briefly discuss **Alternating Current (AC)**.

Answer 25

**Alternating Current (AC)** is an uninterrupted bidirectional flow of charged particles, often associated with alternating voltages. One of the most common forms of alternating waveform is the **sine wave**.

Question 26

Briefly discuss **resistors** and **resistance**.

Answer 26

**Resistors** are **components** whose main characteristic is that they provide **resistance** between their two **electrical terminals**. The **resistance** of a circuit represents its opposition to the flow of **electric current**. The unit of **resistance** is the **ohm (Ω)**. The **ohm (Ω)** is defined as the **resistance** of a **circuit** in which a **current** of 1 **amp** produces a **potential difference** of 1 **volt**.

Question 27

Briefly discuss **Conductance**.

Answer 27

The **conductance** of a **circuit** is its ability to allow the flow of **electricity**. The **conductance** of a circuit is circuit is equal to the reciprocal of its **resistance** and has the units of **siemens (S)**.

Question 28

Briefly discuss **Capacitors**.

Answer 28

**Capacitors** are components whose main characteristic is that they exhibit **capacitance** between their two **terminals**. **Capacitance** is a property of **two conductors** that are **electrically insulated** from each other, whereby **electrical energy** is **stored** in an **electric field** that is created between the two **conductors**. **Capacitance** is measured in **Farads (F)**.

Question 29

Briefly discuss **Inductors**.

Answer 29

**Inductors** are components whose main characteristic is that they exhibit **inductance** between their two **terminals**. **Inductance** is the property of a coil that results in an **e.m.f.** being induced in the coil as a result of a change in the current in the coil. Like **capacitors**, **inductors** can store **electrical energy** and in this case it is stored in a **magnetic field**. The unit of **inductance** is the **henry (H)**.

Question 30

Express the relationship between **voltage (V)**, **current (I)** and **resistance (R)**.

Answer 30

**Ohm's Law** states that the **current** ***I*** flowing in a **conductor** is directly proportional to the applied **voltage *V*** and inversely proportional to its **resistance *R***. V = IR I = V/R R = V/I

Question 31

Define and explain **Kirchhoff's Current Law**.

Answer 31

"At any instant, the **algebraic sum** of all the **currents** flowing into any **junction** in a circuit is zero." **Σ I = 0** If we assume for example that **current** flowing into a **junction** is **positive**, then we can take from this that any **current** flowing out of a **junction** is **negative**. Furthermore, the sum of the **current** flowing into a **junction** is equal in magnitude to the sum of the **current** flowing out of a **junction**. A **junction** is any point where **electrical** paths meet. The law come about from consideration of **conservation of charge** (the charge flowing into a point must equal that flowing out).

Question 32

Briefly discuss **Kirchhoff's Voltage Law**.

Answer 32

"At any instant, the algebraic sum of all the voltages around any loop in a circuit is zero." **Σ V = 0** The term **loop** refers to any **continuous path around the circuit**, and the law comes about from consideration of **conservation of energy**. It is important that the various quantities are assigned the correct sign. Assuming for example that *clockwise* voltages are considered **positive** then *counter**clockwise* voltages must be**negative**.

Question 33

Discuss the instantaneous power dissipation ***P*** of a resistor. i.e. the relationship of ***P***, ***V*** and ***I***

Answer 33

The instantaneous **power** dissipation ***P*** of a **resistor** is given by the **product** of the **voltage** across the **resistor** and the **current** passing through it. ***P = VI*** Combining with **Ohm's Law** gives a range of expressions: ***P = I²R*** ***P = V²/R***

Question 34

How do you calculate the **resistance** of a number of **resistors** in series?

Answer 34

The effective **resistance** of a number of **resistors** in series is equal to the **sum** of their individual **resistances.** **R = R₁ + R₂ + R₃ + ... + R_n**

Question 35

How do you calculate the **resistance** of a number of **resistors** in **parallel**?

Answer 35

The effective **resistance** of a number of **resistors** in **parallel** is given by the following expression: **1/R = 1/R₁ + 1/R₂ + 1/R₃ + ... + 1/R_n** Note: the effective resistance of a number of resistor in parallel will always be less than that of the lowest-value resistor.

Question 36

What is the difference in the **current** that runs through **resistors** connected in **series**?

Answer 36

When several **resistors** are connected in **series** the **current** flowing through each **resistor** is the same. The **magnitude** of this **current** is given by the **voltage** divided by the **total resistance**. e.g. If three resistors are connected in series then the current is given by: **I = V / (R₁ + R₂ + R₃)**

Question 37

How do you determine the **voltage** across a **resistor** in **series** with other **resistors**?

Answer 37

The **voltage** across a given **resistor** in series is given by the **current** multiplied by the **resistance** of that **resistor**. **V₁ = IR₁** Given that the **current** is given by the total **voltage** divided by the sum of the **resistances**, we can use this as follows: **V₁ = IR₁ = ( V / [R₁ + R₂ + R₃] ) R₁** We can take from this that the fraction of the total voltage across each resistor is equal to its fraction of the total resistance. e.g. **V₁ / V = R₁ / (R₁ + R₂ + R₃)**

Question 38

What is the unit of **e.m.f.** and how is it defined in terms of **energy** and **charge**?

Answer 38

The unit of **e.m.f.** is the **volt (V)**. The **volt** is defined as the **potential difference** between two points when one **joule (J)** of **energy** is used to move one **coulomb (C)** of **charge (Q)** from on point to the other.