1 © Unitec New Zealand Electrical and Electronic Principles ENGG DE4401 Topic 1 : I NTRODUCTION TO E LECTRICAL AND E LECTRONICS PRINCIPLES

Topic overview Physics and physical quantities Engineering approach –Lumped Circuit Abstraction Current, Voltage, Resistance, Power –difference between electron flow and conventional current flow Measurements –Units, Metric conversion, Scientific notation, Graphs and tables Resistors Ohm’s Law 2 © Unitec New Zealand

Electricity We are interested in electricity: a phenomena related to the charged particles, the forces between them and their movement. –Chapter 1 Schaum’s Basic Electricity book 3 © Unitec New Zealand

Engineering problems... We want to answer this question: Will this light bulb glow? We cannot see the electrons, but we can measure their movement in the form of electric current (I) and we can measure the potential energy that initiate that current flow. 4 © Unitec New Zealand

.. require engineering approach: Abstraction We do not care about –Length of the wire in the light bulb –Light bulb filament –The temperature of the light bulb, etc. We replace physical item with a discrete element as if the physical property (resistance of the light bulb, R, battery voltage V) is concentrated in a single point and we can access it across its terminals (A and B in the Fig below). Now we observe only the key issue: the power delivered to the load. 5 © Unitec New Zealand

Lumped Circuit Abstraction (LCA) We are working with discrete elements (components) and each has a physical quantity describing it. 6 © Unitec New Zealand

Electric circuit An electric circuit is formed when a closed conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current The electromotive force which “motivates” electrons to "flow" in a circuit is called voltage or emf. 7 © Unitec New Zealand

Basic Definitions: Current The movement or the flow of electrons (charge) is referred to as current. Current is represented by the letter symbol I ( it stands for “intensity”). Current is the rate of flow of electrons through a conductor. The basic unit in which current is measured is the ampere (A). –One ampere of current is defined as the movement of one coulomb ( quantity of charge) past any point of a conductor during one second of time. An instrument called an ammeter is used to measure current flow in a circuit. 8 © Unitec New Zealand

Basic Definitions: Voltage An electric charge has the ability to do the work of moving another charge by attraction or repulsion. The ability of a charge to do work is called its potential. Voltage is a measure of potential energy, always relative between two points (potential difference). –The symbol for voltage is V, (emf can be e or E). –The basic unit for voltage or emf is the volt ( V ). Remember: Voltage is always relative between two points: –What is the meaning of a battery voltage output of 6 V? –A voltage output of 6V means that the potential difference between the two terminals of the battery is 6V. 9 © Unitec New Zealand

Analogy –water in pipes 10 © Unitec New Zealand

We adopt symbols and conventions 11 © Unitec New Zealand

Electron and Conventional current flows Electric current flow is the movement of ‘free’ electrons along a conductor. Electrons are negative charges. Negative charges are attracted to positive charges. Electrons move from the negative terminal of a battery to the positive terminal. This is called electron current flow. Another way to look at electric current flow is in terms of charges. Electric charge movement is from an area of high charge to an area of low charge. A high charge can be considered positive and a low charge negative. With this method, an electric charge is considered to move from a high charge (positive or +) to a low charge (negative or -). This is called conventional current flow. 12 © Unitec New Zealand

We choose conventional flow! Conventional current flow is a standard adopted in NZ industry and we will use it from now on. 13 © Unitec New Zealand

Resistance Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is called resistance. Resistance R is measured in ohms: Ω Opposite of the resistance is conductance G: G = 1 / R Conductance G is measured in Si (siemens), but sometimes the unit used is mho (opposite of ohm, used for R) 14 © Unitec New Zealand

Calculating Resistance 15 © Unitec New Zealand Resistance depends on : Type Material of which the conductor is made (a constant ρ called Specific Resistance or resistivity) Dimensions of the conductor Shape of the conductor For a piece of material with cylindrical shape:

Resistors Special components called resistors are made for the express purpose of creating a precise quantity of resistance for insertion into a circuit. Two common schematic symbols for a resistor are 16 © Unitec New Zealand

Resistors value 17 © Unitec New Zealand A resistor colored Yellow-Violet-Orange-Gold would be 47 kΩ with a tolerance of +/- 5%.

Resistors in circuits © Unitec New Zealand

Don’t confuse them with inductors This is an inductor (see L201 written on the side?) 19 © Unitec New Zealand These are resistors: the standard beige/brown ones are carbon film and metal film resistors are often blue.

Surface mount resistors 20 © Unitec New Zealand

How to get a law? Measurements Using an instrument (multimeter) we can measure voltage, current, resistance. 21 © Unitec New Zealand

Units International standard of units is called SI (systeme internationale). There are seven “base” units from which all other units are derived: 22 © Unitec New Zealand

Physical quantities and units of measure 23 © Unitec New Zealand All of these symbols are expressed using capital letters. However, if a quantity is changing in time, we use small letter (called an "instantaneous" value). Direct-current (DC) values will be in capital letters, for AC (alternate current) values we use small letters.

Scientific notation Sometimes we work with very small or very large values. To avoid writing large number of zeros, we introduce Scientific notation, using powers of number © Unitec New Zealand

Metric prefixes We go step further, and introduce code words for frequently used scientific notations (multiples of 3). We use these words as prefixes to our Units 25 © Unitec New Zealand

For practice: Book Schaum’s Outline of BASIC ELECTRICITY Chapter 2, pages © Unitec New Zealand

Your multimeter Make sure your leads are connected to the right plug: –You may damage your mulitmeter if you are not using it properly! Rotating switch must be on the right field: chose between DCV, AC V, A or Ohm –Chose higher range for current and than reduce it, if needed. Do not touch the tip of the probe while measuring! 27 © Unitec New Zealand

Measuring resistance Your multimeter is now an Ohmmeter Make sure your ohmmeter range is correct. 28 © Unitec New Zealand Important: measuring resistance must only be done on de-energized components! When the meter is in "resistance" mode, it uses a small internal battery to generate a tiny current through the component to be measured. If there is any additional source of voltage in the loop, faulty readings will result. In a worse-case situation, the meter may even be damaged by the external voltage.

Exercise 1: Measuring resistance For all three offered resistors, do the following: –Select a resistor from the assortment –Set your multimeter to the appropriate resistance range –Measure the resistance using your multimeter: Be sure not to hold the resistor terminals when measuring resistance, or else your hand-to-hand body resistance will influence the measurement! –Record measured resistance value in the table. –Confirm the value by reading the color code from the chart. 29 © Unitec New Zealand

Measuring voltage and current Current : –Always measured with multimeter connected in series. –Connecting in series means you must break the circuit to insert the multimeter (so the current flowing in circuit goes through meter). Voltage –measured with multimeter connected in parallel to the component. Series or parallel? Clue: the current will split in two paths for parallel circuit. In the series circuit, there is only one current path) 30 © Unitec New Zealand

Measuring current Multimeter is now working as an Ammeter. It must be connected in series, Make sure the plug is in Amp hole, not in VΩ hole! Choose DC or AC, as needed: we measure DC current 31 © Unitec New Zealand

Measuring voltage Multimeter is now working as an Voltmeter. It must be connected in parallel Make sure the plug is in VΩhole, not in Amp hole! Be careful not to touch the bare probe tips together while measuring voltage, as this will create a short-circuit! 32 © Unitec New Zealand

Measured value: in Table or Graphs 33 © Unitec New Zealand

Exercise 2: Measuring voltage and current Aim: to observe the change of the current through a 1kΩ resistor when the voltage on the resistor is varied. 34 © Unitec New Zealand

IV characteristics for an ideal resistor 35 © Unitec New Zealand

Formula Graph is good for representing unknown relationships, but sometimes relationship between two values is simple and easier to describe using a mathematical formula. That is true for our example with current and voltage across the resistor and the formula is called Ohm’s law: 36 © Unitec New Zealand

Ohm’s Law Ohm's Law describes relationship between current, voltage and resistance. Georg Simon Ohm discovered that the amount of electric current through a metal conductor in a circuit is directly proportional to the voltage impressed across it, for any given temperature. That constant of proportionality is called resistance. 37 © Unitec New Zealand

Using Ohm’s Law in circuit analysis Ohm’s law is expressed in the form of a simple equation: V = I R If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third. 38 © Unitec New Zealand V = R I I = V / R R = V / I

Solution: how to find current I 39 © Unitec New Zealand

Find R... What is the amount of resistance (R) offered by the lamp? 40 © Unitec New Zealand

Solution for R 41 © Unitec New Zealand

Find E... In the last example, we will calculate the amount of voltage supplied by a battery, given values of current (I) and resistance (R): What is the amount of voltage provided by the battery? 42 © Unitec New Zealand

Solution for E © Unitec New Zealand

Maths revision: Algebra How to use a formula Manipulate the formula to find unknown value Fractions Indices 44 © Unitec New Zealand

Moodle quiz 1 Please work on Moodle quiz 1 If you find questions challenging, read the notes in this presentation and practice the examples from Schaum’s Basic Electricity. If it is still not clear, write it down and bring it up first thing next class. 45 © Unitec New Zealand