The Electrical Circuit - Engineering - ثاني ثانوي

2. Electrical Engineering In this unit, we will learn the basics of electrical circuits. We will also learn about the different types of electrical circuits. Finally, we will use a simulation program to understand how circuits operate. Ministry of Education 26 2024-1446 Learning Objectives In this unit, you will learn to: > Describe the basic properties of electrical circuits and electrical quantities. > Distinguish between DC and AC electric currents. > Understand how Ohm's law is applied to electrical circuits. > Demonstrate how to connect resistors in an electric circuit. > Design electrical circuits. > Simulate electrical circuits using Multisim Live. Tools > Multisim Live

Lesson 1 The Electrical Circuit The basics of Electricity In this lesson, we will examine some basic concepts that are used in the design of electrical circuits. We will also demonstrate the means by which we study their functions. Current The electric current in metallic conductors consists of electrons (e), which are very small particles that carry the elementary negative (-) electric charge, and the current moves at very high speeds. Link to digital lesson www.ien.edu.sa Amperes To quantify the motion of electrons, André-Marie Ampère created the concept of how many electrons pass through a point in the circuit in one unit of time. He called this electric current, or intensity of current (I), which is measured in amperes (A). 1A= 1 coulomb 1 second Volt In order for an electric current to move in a circuit, we must create a potential difference, also called a voltage (V). This shows us how much energy is used in moving one coulomb of electric charge inside the circuit. وزارة التعليم Ministry of Education 2024-1446 1V = 1 joule 1 coulomb SMART TIP The volt is the unit of electric voltage, and 1 volt is denoted as 1V and is the measure of the potential difference when an electric current of 1 ampere (A) flows through an element of 1 ohm (2) resistance. 27

Table 2.1: Electrical quantities table Electrical quantity Electrical Energy Unit of measurement joule (J) coulomb (C) Electric charge Electric Current ampere (A) Voltage volt (V) Resistance Electric power ohm (Q) watt (W) The components of an electrical circuit are built from materials that facilitate the movement of electrons, which means electric current can flow through them. These materials are called conductors. For example, metals are conductors. Core Hardware Components of an Electrical Circuit Power Source We create a voltage between two points on the electrical circuit with a power source. The source works to transfer electrons from one point in the circuit to another. Two poles are created, one with an electron deficit (+) and the other with a surplus (-). The balance in the quantities of electrons needs to be restored. To achieve this, electrons are drawn from the negative pole (-) to the positive pole (+). This movement generates electricity. 4 The power source can be a battery or a generator. Alternating Current (AC) and Direct Current (DC) The source is constructed so that the electric current either moves in a constant direction from the negative to the positive pole (DC) or in an alternating direction back and forth between the poles (AC). DC usually flows at low voltages and the electrons move from (-) to (+), but we consider conventional motion to be from (+) to (-). The electricity supply network of a city uses AC voltage for lights and home appliances. Electronic devices like computers and smartphones require low DC voltage. A DC power supply converts the AC voltage to a lower DC voltage. وزارة التعليم Ministry of Education 28 ZU24-1446 Power supply

Resistor As mentioned before, electric current is the movement of electrons through an electrical wire. Resistors (R), as their name suggests, resist this movement. They do not stop it, they merely slow the movement down. The faster the electrons move, the greater the electrical energy of the system. The energy carried by the electrons is converted into heat by resistors. Resistance, measured in ohms, is defined in terms of the ratio of voltage to current. If a current of 1A flows through a resistor when a voltage of 1V is applied to it, its resistance is 1 ohm. 1 V 1 ohm = 1 A Figure 2.1: Photo of resistors If we have two or more resistors, then we give them names, such as R1, R2, R3... CE 415V-10000 50/60Hz 3 CE CE Switch A switch (or circuit breaker) must be used in each circuit to control whether or not electricity flows through the circuit. D-OFF -ON 1-ON 00000 Figure 2.2: Different types of switches and circuit breakers وزارة التعليم Ministry of Education 2024-1446 This is a circuit breaker. INFORMATION Resistance is denoted by the Greek letter omega in capitals: Q (ohm). ON OFF 2 29

Instruments for Measuring Electrical Quantities Various instruments have been invented for measuring the different electrical quantities. These include: The voltmeter, which is connected in parallel with a conductor and measures the voltage across its ends. DO.O 10A The ammeter, which is connected in series with the conductor and measures the intensity of the current flowing through the conductor. Figure 2.3: Multimeter The ohmmeter, which measures the resistance of a conductor. The multimeter, which is an instrument that can measure voltage, current and resistance. A multimeter is a tool that can measure the values of current, voltage, and resistance across various parts of an electrical circuit. It is mainly used for troubleshooting. A lamp behaves like a resistor. Electrical Circuit Components Before creating our first electrical circuit, let's look at the basic components we will need: Electrical Components Circuit •⚫Symbols وزارة التعليم Ministry of Education 30 2024-1446 Source Switch 4/F مة Resistor

What the Colors on a Resistor Mean Fixed resistors use standard color-coding rules to visually represent the basic properties of a resistor. The number of colored bands on a resistor show whether it is a standard or high precision resistor. 4 bands means a standard-precision resistor, whereas 5 bands means a high-precision resistor and 6 bands is essentially a 5 band resistor but with an extra ring that denotes the temperature coefficient. How to decode bands on a standard-precision resistor: > The 1st, 2nd, 3rd and 4th bands denote the resistor's value. > The 5th band denotes the resistor's tolerance with a standard measurement error of within 5% to 10% of the real tolerance value of the resistor. Let's take a look at resistor color codes: COLOR 1st DIGIT 2nd DIGIT 3rd DIGIT MULTIPLIER TOLERANCE BLACK 0 0 0 1Ω TEMPERATURE COEFFICIENT 250 ppm/K BROWN 1 1 1 10 Ω ± 1% 100 ppm/K RED 2 2 2 100 Ω ± 2% 50 ppm/K ORANGE 3 3 3 1 ΚΩ 15 ppm/K YELLOW GREEN BLUE VIOLET 7 60 16 4569 4 4 10 ΚΩ 25 ppm/K 5 5 100 ΚΩ 0.5% ± 20 ppm/K 1 ΜΩ 0.25% ± 10 ppm/K 7 7 0.1% ± 5 ppm/K GREY 8 8 8 1 ppm/K WHITE 9 9 9 GOLD 0.1 Ω 5% ± SILVER 0.01 Ω 10% ± Figure 2.4: Resistor color coding INFORMATION Not all resistors exert the same amount of resistance on the flow of electrons. The main rule is that the greater the resistance, the more the intensity of the electric current is diminished. قرارة التعليم Ministry of Education 2024-1446 31

4-BAND 5-BAND 6-BAND 1 2 x105 ±5% =1,200 kQ ± 5% 100x10² ±1% 2 7 4 x10° ±2% 250 = 10,000 ± 1% Figure 2.5: Examples of resistor calculation using color codes =274 ± 2%, 250 ppm/K Resistor Connections in Electrical Circuits In an electrical circuit the resistors are connected as follows: Resistor connections In series R1 R₂ 1ΚΩ 1ΚΩ Description Resistors R₁ and R₂ have one common end, the same current I flows through them and have voltages V₁ and V2 across their ends. Where V₁ + V₂ = V₁₁ T' In parallel R₁ 1ΚΩ R₂ 1ΚΩ Resistors R1 and R2 have two common ends, have the same voltage V across their ends and 2 different currents flow through them, I₁ and 12. Where I₁ + I2 = 1,. Table 2.2: Prefixes of Units of Measurement Name Symbol Factor ليم وزارة الا Ministry of Education 32 ZU24-1446 nano micro milli kilo mega giga μ m k M G 10-9 10-6 10-3 10³ 106 109 Total resistance R₁ = R₁ + R₂ 1 1 1 + RT R₁ R₂ Total resistance is the resistance generated by all the resistors in a circuit.

Electrical Circuit Connections All components of a circuit offer some resistance to current depending on their use. In the following circuit we have: A lamp denoted by X, operating normally at 12V voltage. • A switch denoted by S. • A 12V power source. Example +1/+ Figure 2.6: Schematic symbols for electrical circuits V 12V Open switch Light bulb off S 12V X Closed switch Light bulb on Each device offers some resistance. For example, the wire in a light bulb resists electron flow. The result of this is the conversion of electricity into heat and light. The internal resistance of switches and power sources is negligible, so they aren't counted in the total resistance of the circuit. V 12 V The 12V label on a light bulb is the value of the voltage that must be applied to its ends for it to function properly. The light emitted and the intensity of the electric current flowing through the lamp are in relation to the rated voltage of the connected battery. Low voltage results in light that is dimmed or even barely visible. Very high voltage may damage the lamp. وزارة التعليم Ministry of Education 2024-1446 S X www INFORMATION Generally, DC sources are much safer than AC sources. 12 V 33

Ohm's Law In electrical circuits, it is important to know the relationship between the electric current flowing through a resistor and the voltage across its ends. The German physicist Georg Simon Ohm first explored this relationship in 1827. He defined that a conductor which has a constant resistance R and a voltage V at its ends allows an electric current of intensity I to flow through the conductor. He observed that the current | is proportional to the potential difference V. In mathematical notation this relation is written as: V R This law can also be applied to a circuit with more than one resistor. Essentially, we view the complete electrical circuit as one resistor itself, by determining the total resistance of the entire circuit. When studying electrical circuits and calculating the values of V, I and R for each component of the circuit, we continuously apply Ohm's law. Series and Parallel Circuit Connections Series and Parallel connections of resistors are shown below: What is a Series Connection? All components in a series circuit are connected end to end, forming a single path for current to flow along, and there is no branching of the electric current. What is a Parallel Connection? Components in a parallel circuit are connected so that there are two or more possible paths for the current, forming two sets of electrically common points, and there is a branching of the electric current. وزارة التعليم Ministry of Education 34 2024-1446

Series Connections Let's start with the series circuit. You have the following values: > R₁ = 30k > R₂ = 60k > Voltage V = 9V supplied by the battery. -M- -M Example R₁ R₂ w ww 30ΚΩ 60ΚΩ V 9V The sum of the voltages, V1 and V2, across each resistor, is equal to the voltage across the ends of the source. We will first calculate the total resistance R of the circuit: R₁ = R₁ + R₂ = 90ΚΩ V 9 Next we will calculate the current I flowing through the circuit: I = = = 0.1mA RT 90ΚΩ Finally, we will calculate the voltages V at the ends of each resistor: V₁IX R₁0.1mA x 30k = (0.1 x 10-3) x (30 x 10³) = 3V V₁ = I× R, ⇒ 0.1mA × 60kN = (0.1 x 10-3) x (60 × 103) = 6V In a wire or cable, the resistance R depends on: > the length: Longer wire means greater resistance. > the thickness: Thicker wire means lesser resistance. > the material that the cable is made from. For example, copper wires have lower resistance. وزارة التعليم Ministry of Education 2024-1446 SMART TIP The lower the resistance of a conductor, the higher the intensity of the current flowing through it, for a given voltage. 35

Parallel Connections Now we will see a circuit whose resistors are connected in parallel. > R₁ = 3kQ > R₂ = 6kQ > V = 9V M --- Example R1 w Node 介 3ΚΩ (11+12)= | V₁ 9V F R₂ w 6k9 The sum of the two currents is equal to the current flowing through the source, in this case the battery. R₁ × R₂ (R₁ + R₂) 18ΚΩ ⇒ R₁T = = 2ΚΩ 9ΚΩ 9V 3ΚΩ 9 3 × 10³ = 3 × 103 = 3mA We will first calculate 1 1 1 the total resistance of the circuit: = + R.p R₁ R = R₁₂ Next we will calculate the V₁ I = ⇒ I₁ = flow of current of R₁: R₁ Next we will calculate the V₂ flow of current of R2: I₂ I. = = R₂ 9V 6kЛ Next we will calculate the flow of current in the circuit: T = 1₁ + I2 ⇒ I Τ We can find the same result for I by applying Ohm's law: = == 9 6 × 10³ = 1.5 x 103 = 1.5mA 3mA 1.5mA = 4.5mA V 9V I = = ⇒ I = = RT 2ΚΩ Node A node is a point in a circuit where 2 or more conductors meet. A circuit loop is a part of the circuit that starts at one point and ends at the same point following the path of current flow. Ministry of Education 36 2024-1446 |1 12 Node 9 2 × 103 = 4.5 × 10-3 = 4.5mA Ohm's law cannot be applied to devices in which the ohmic resistance does not remain constant. Examples include diodes, transistors, etc.

Ohm's Law: Example Problem In this example, we want to find the potential difference, or voltage, between points A and B. You can find the total resistance of the circuit between points A and B: R₁ w 11Ω R3 www 492 A V B R₂ 1892 First we note that resistors R3,R4 and R5 are connected in series, so: R3,R,R5= 4 + 8 + 6 = 18N R5 ww 69 We can now consider an equivalent circuit: وزارة التعليم Ministry of Education 2024-1446 > R₁ www 11Ω R4 892 R₁₂ + R₁ + R5 4 R₂ R3.4.5 1892 1892 37

In the equivalent circuit, we observe that R3,4,5 and R₂ are connected in parallel. www R1 |1 11Ω Resistors in parallel IT 12 V IT Therefore: R₂//R3,4,5 R3,4,5 × R2 (R3,4,5 + R2) = 90 R2 1892 So we consider the following equivalent circuit: www R₁ R₂// R 3,4,5 11Ω = V ww R2,3,4,5 R3,4,5 1892 We can calculate the voltage between points A and B, if the current flowing through R₂ is 12=1A. So the voltage across the ends of R₂ will be: V₂ = I2 × R₂ I2 x R₂ = 1 × 18 = 18V Since the resistor R3,4,5 is connected in parallel, with R2 and therefore has a voltage of V3,4,5 = 18V. 992 V 3,4,5 18 So I 3,4,5 = 1A = R3,4,5 18 From this, we find the total resistance: R₁ = R₁ + R2,3,4,5= 11 + 9 = 20£ A > B 40V وزارة التعليم 38 Ministry of Education 2024-1446 w The current flowing through the source and R₁ is: IT = = 12 + 13,4,5 Τ = 1+1=2A Thus, the voltage across A and B is: V = I × R = = 2 × 20 = 40V AB RT 2092 Voltage between the points AB

Exercises 1 Tick the correct sentences below. A resistor is connected to the poles of a generator that has negligible internal resistance. If we connect another identical resistor in series with the first resistor, then the intensity of the current: True False 1. Will double. 2. Will remain constant. 3. Will drop to half. 4. Will quadruple. 2 Tick the correct sentences below. When two resistors, R₁ and R2, with different resistances are connected in parallel: 1. They display the same voltage at their ends. 2. A current of equal intensity flows through each. 3. Their equivalent resistance is R₁ from the equation R₁ = R₁ + R₂. 4. Currents of different intensities flow through each. وزارة التعليم Ministry of Education 2024-1446 True False 39

4 3 Read the sentences and tick ✔ True or False. True False 1. An ammeter measures voltage. 2. A voltmeter is connected across a branch in the circuit. 3. The energy that the electric current transmits to a resistor is completely converted into thermal energy. 4. Resistors connected in series have the same current flowing through them. 5. R₁ = R₁ + R₂+ R3 +... + R holds true for resistors connected in series. T n 6. Resistors that are connected in parallel display the same voltage at their ends. 7. A voltmeter measures the intensity of current. 8. For resistors that are connected in parallel, the total resistance of the circuit is R = R₁ + R₂ + R3 +... + R^ T Match the items in the first column with those in the second. وزارة التعليم Ministry of Education 40 2024-1446 Quantities Resistance Units V Voltage W Electrical energy J Power Ω

5 On a piece of paper, draw a circuit consisting of two identical light bulbs X₁ and X₂, the source V and the switch S in series. Closing the switch, electric current begins flowing through the circuit. Determine whether the two light bulbs X₁ and X₁₂ will emit the same amount of light. Justify your answer. 6 Three resistors R₁ = 2002, R₂ = 502 and R3 = 402, are connected in parallel to a voltage V = 20V. The resistor R2 is connected to an ammeter in series which shows the current 12 that flows through R2. The source is connected to a switch S and a second ammeter in series, which shows the intensity of the current I, which flows through the source. The resistances of the power source and the ammeters are considered negligible. 1. Draw the circuit diagram. 2. Find the total resistance R_. 3. Find the ammeter readings when switch S is closed. وزارة التعليم Ministry of Education 2024-1446 41

7 In the circuit diagram, the source has voltage V. The power source and the two measurement instruments, the ammeter (A) and voltmeter (V), have negligible internal resistances. The resistors have values R₁ = 1000, R₂ = 5002, R3 = 500, and the ammeter displays a reading of 0.8A. Calculate the following: 1. The total resistance of the circuit. 2. The intensity of the current flowing through each resistor. 3. The voltmeter reading. R₁ A R3 R2 V V Use the physics laboratory and try to apply it practically under the supervision of the teacher or the assistant, then explain how both the ammeter and the voltmeter are connected to the electrical circuit. وزارة التعليم Ministry of Education 42 2U24 -1446