Lesson 2 - Electricity.pdf

Basics of Electricity Lesson 2 Learning Objectives At the end of this lesson, you will be able to: Explain the difference between voltage, current, and resistance; Explain the two direction of current; Explain the two types of current; Explain Ohm’s Law; Expla...

Basics of Electricity Lesson 2 Learning Objectives At the end of this lesson, you will be able to: Explain the difference between voltage, current, and resistance; Explain the two direction of current; Explain the two types of current; Explain Ohm’s Law; Explain the two types of circuit; Compute for the voltage, current, and resistance of a circuit using Ohm’s Law; Introduction Have you ever wondered what happens when lightning strikes to the ground? Or what causes lightning? According to National Geographic, lightning is an electrical discharge caused by imbalances between storm clouds and the ground, or within the clouds themselves. Most lightning occurs within the clouds. Each lightning bolt can contain up to one billion volts of electricity. About 2,000 people are killed worldwide by lightning strikes each year. Fun Fact! 01 Let’s Discover! “I have not failed. I’ve just found 10,000 ways that won’t work.” —Nikola Tesla What is Electricity? Electricity is the movement of electrons. Electrons create charge, which we can harness to do work. Electric Circuit A closed conducting path where charges flow. Three Essential Elements in an Electric Circuit Voltage Current Resistance Get to Know… Michael Faraday A British Scientist who discovered the basic principles of electricity generation during the 1820s and early 1830s. Electric Current Electric current is the amount of charge passing through any point in a conductor per unit time. The SI unit of current is the Ampere (A) named after the French scientist and mathematician André Marie Ampère. In symbols: q I= t where I is the current in ampere, q is the charge in coulombs, and t is the time in seconds. Hence, 1A = 1 C/s 1 coulomb = approximate 6.24 x 1018 electrons Direction of Current Electric current constitutes a flow of charges. But which charges, the positive or negative charges? Conventional Current Electron Current Conventional Current the direction of flow is from positive to negative. Electron Current is a stream of electrons flowing in a direction opposite that of the conventional current. The electron current is just equivalent of the conventional current. The conventional current is still followed. Types of Current There are two types of current: Direct current Alternating current Direct Current a current that flows in one direction at all times. Direct current or dc is used in battery-operated devices such as flashlights, calculators, automobiles, and cellular phones. Alternating Current a current that changes directions at regular intervals (normally 60 times in one second). Alternating current or ac is produced by electric companies, like PALECO, to power most of our appliances. Get to Know… André Marie Ampère A French Physicist and Mathematician often referred to as the “Isaac Newton of Electricity”. He was the first to describe current as a continuous flow of electricity along a wire. Voltage (Potential Difference) In order for charges to flow from one point to another, a difference of potential must exist between these two points. Potential difference is the amount of energy needed to move a charge of one coulomb from one point to another. This energy is usually referred to as voltage in an electrical circuit. The unit of potential difference is the volt, represented by a capital letter V. The unit “volt” is named after the Italian physicist Alessandro Volta who invented what is considered the first chemical battery. Earth or ground is an electrically neutral body. It has equal number of negative and positive charges. Earth is considered to be at zero potential and is used as a reference for voltage measurements. Voltage (Potential Difference) The source of potential difference in a circuit is usually a cell. The standard symbol of a cell in an electric circuit is shown below. The longer vertical line is the positive terminal, while the shorter one is the negative terminal. The positive terminal is at a higher potential than the negative terminal. The voltage across the terminals of a cell is called electromotive force (EMF). An electric cell consists of one positive electrode and one negative electrode. These electrodes are immersed in an ion-conducting medium called electrolyte. Voltage (Potential Difference) The source of potential difference in a circuit is usually a cell. The standard symbol of a cell in an electric circuit is shown below. The longer vertical line is the positive terminal, while the shorter one is the negative terminal. The positive terminal is at a higher potential than the negative terminal. The voltage across the terminals of a cell is called electromotive force (EMF). An electric cell consists of one positive electrode and one negative electrode. These electrodes are immersed in an ion-conducting medium called electrolyte. Additional Knowledge Combination of Cells Combination of Cells A battery is a combination of cells. Cells may be connected in series or parallel. Series Connection of Cells Cells are in series when the positive terminal of one cell is connected to the negative terminal of the next cell and so on. For example, if you have four cells with 1.5V each connecting them in series will result to total voltage of 6V. Cells are connected in series when you want a bigger voltage. Parallel Connection of Cells Cells are in parallel when all the positive terminals are joined together as well as the negative terminals. For example, if you have four cells with 1.5V each connecting them in parallel will result to total voltage of just equal to the voltage of one cell. Cells are connected in parallel when you want more current. As a general rule, only identical cell must be connected in parallel. Get to Know… Alessandro Volta An Italian Scientist whose skepticism of Luigi Galvani's theory of animal electricity led him to propose that an electrical current is generated by contact between different metals. Volta's theoretical and experimental work in this area resulted in his construction of the first battery, the voltaic pile.. Resistance Resistance is the opposition a material offers to the flow of charges through it. The SI unit of resistance is ohm, named after Georg Simon Ohm. The Greek letter omega Ω is used to represent the unit ohm. Two symbols may be used for a resistor in an electric circuit. Additional Knowledge Factors Affecting Resistance of an Object Four factors affecting resistance of an object Cross-sectional area Length Kind of material Temperature Cross-sectional area Resistance varies inversely to the cross-sectional area of the object. As the area increases, the resistance decreases. A good example for this is a road. The wider the road, the less “resistance” it will offer to the flow of traffic along it. Length The resistance of an object varies directly to its length. An increase in length increases the resistance. A longer wire offers greater resistance than a shorter wire. Kind of Material and Temperature Resistance varies with temperature. As temperature increases, resistance increases for conductors and decreases for insulators and semiconductors. For superconductors, resistance first decreases as temperature decreases just like ordinary conductors. But at a certain temperature, resistance drop to zero. How are voltage, current, and resistance related in an electrical circuit? A simple answer to this question is the Ohm’s Law. Ohm’s Law In 1827, Georg Simon Ohm experimentally established the relation among electric current, resistance, voltage in an electric circuit. He found out that the current passing through a conductor varies directly to the voltage applied at its ends, and inversely to the resistance of the conductor. Ohm’s Law may be applied to the whole circuit or to a particular part of a circuit. Ohm’s Law When applied to a whole circuit, 𝐸𝑀𝐹 𝐼𝑇 = 𝑅𝑇 where 𝐼𝑇 is the total current, EMF is the electromagnetic force or the voltage of the cell or battery, and 𝑅𝑇 is the total resistance of the circuit. Ohm’s Law When applied to a portion of the circuit, 𝑉 𝐼= 𝑅 where I is the current in ampere (A) passing through that part of the circuit, V is the potential difference in volts (V), and R is the resistance in ohms (Ω) of the same part of the circuit. Ohm’s Law Formula For you to easily remember the formula for Ohm’s Law, use the illustration below. Ohm’s Law Formula If you will calculate the voltage of the same part of the circuit cross-out the V which represents voltage. The vertical line that separates I and R means multiplication. Therefore, your formula for getting the voltage is V = I x R. Ohm’s Law Formula To calculate the resistance of the circuit, cross-out R which represents resistance. The horizontal line that separates V and I means division as shown in Figure 8. Therefore, your formula for getting the resistance is R = V/ I. Ohm’s Law Formula To calculate the current of the circuit, cross-out I which represents current. The horizontal line that separates V and R means division. Therefore, your formula for getting the current is I = V / R. Sample Problems 1. The resistance of a 150 cm piece of wire is 40 Ω. The wire is divided into 5 pieces, each with a length of 30 cm. What is the resistance of each piece of wire? 2. Wire A has a resistance of 50 Ω. What is the resistance of wire B if its cross- sectional area is twice that of wire A? Assume that wires A and B are made of the same material with equal lengths. Solution Problem 1 Recall that if two quantities are directly proportional to each other, then their ratio must be constant. Therefore, since resistance of a wire is directly proportional to its length, = constant or equivalently to 𝐿1 = 𝑅 𝑅 𝑅2 𝐿 1 𝐿2 40 Ω 𝑅2 Substituting the values, = 150 𝑐𝑚 30 𝑐𝑚 Solving for 𝑅2 , 𝑅2 = 8 Ω Solution Problem 2 Recall that if two quantities are inversely proportional to each other, their product must be constant. Therefore, since resistance of a wire is inversely proportional to its cross-sectional area, RA = constant where A is the cross-sectional area or equivalent to 𝑅1 𝐴1 = 𝑅2 𝐴2 Let 𝐴1 and 𝐴2 be the cross-sectional areas of wire A and wire B, respectively. 𝐴2 = 2𝐴1 Substituting values, 50 Ω (𝐴1 ) = 𝑅2 (2𝐴1 ) Solving for 𝑅2 , Analyzing Simple Circuits using Ohm’s Law Let’s use these equations to help us analyze simple circuits. There is only one source of voltage (the battery, on the left) and only one source of resistance to current (the lamp, on the right). This makes it easy to apply Ohm’s Law. If you know the two values of any of the three quantities (voltage, current, and resistance) in this simple circuit, you can use Ohm’s Law to compute for the third.  Let’s use these equations to help us analyze simple circuits. What is the amount of current in this circuit? 𝑉 𝐼= 𝑅 V = 15 V R=5Ω 15 𝑉 𝐼= 5Ω 𝐼 = 3𝐴 Let’s use these equations to help us analyze simple circuits. What is the amount of I = 10 A resistance given by the lamp? 𝑉 𝑅= 𝐼 V = 50 V 50 𝑉 𝑅= 10 𝐴 𝑅 = 5Ω I = 10 A Let’s use these equations to help us analyze simple circuits. What is the amount of voltage I=3A provided by the battery? 𝑉 = 𝐼𝑅 𝑉 = (3 𝐴)(10 Ω) V = ??? R = 10 Ω 𝑉 = 30 𝑉 I=3A Analogy of a Simple Circuit A simple circuit consisting of battery, resistors, and current or flowing charges could be compared to the flow of blood in the circulatory system. The heart is the battery that pumps blood to the different parts of the body, the current is the blood, the resistors are the frictional forces encountered while the blood is flowing or perhaps the deposits in the arteries, and the veins and the arteries are the connecting wires. Two Types of Circuits Series Circuit - is one that contains more than one piece of electrical apparatus (or resistor) connected one after another in a single line. In series circuit, the current flows in a single path and is the same in all parts, regardless of resistance. The current stops flowing whenever a part of a circuit fails. Christmas tree lights are normally connected in circuits. Parallel Circuit - is one where two or more pieces of electrical apparatus (or resistors) are connected side-by-side so that the current is divided between them. In such a circuit, each apparatus operated independently of the others. Hence, even if one piece of apparatus fails, the current still flows through the others. Household appliances are usually connected in parallel. Laws of Series and Parallel Circuits Sample Problem A 20.0 Ω resistor is connected in series with a 5.0 Ω resistor, with a 50.0 V across the combination. Find the total current passing through the combination. Solution We are given R1 = 20.0 Ω and R2 = 5.0 Ω RT = 20 Ω + 5 Ω = 25 Ω Using Ohm’s Law 50 V = IT (25 Ω) IT = 2.0 A Series and Parallel Circuits Get to Know… Georg Simon Ohm A German physicist born in Erlangen, Bavaria, on March 16, 1789. As a high school teacher, Ohm started his research with the recently invented electrochemical cell, invented by Italian Count Alessandro Volta. Using equipment of his own creation, Ohm determined that the current that flows through a wire is proportional to its cross-sectional area and inversely proportional to its length or Ohm's law.  02 Wrap-up Review Electricity is the movement of electrons. A closed conducting path where charges flow is called an electric circuit. Three essential elements in an electric circuit: Voltage or potential difference Current Resistance Review Electric current is the amount of charge passing through any point in a conductor per unit time. The SI unit of current is the Ampere (A) named after the French scientist and mathematician André Marie Ampère. Direction of Current Conventional current - the direction of flow is from positive to negative. Electron current - is a stream of electrons flowing in a direction opposite that of the conventional current. Review Types of Current Direct current - a current that flows in one direction at all times. Alternating current - a current that changes directions at regular intervals. In order for charges to flow from one point to another, a difference of potential must exist between these two points. Potential difference is the amount of energy needed to move a charge of one coulomb from one point to another. Review Resistance is the opposition a material offers to the flow of charges through it. Four factors affecting the resistance of an object: Cross-sectional area Length Kind of material Temperature Review In 1827, Georg Simon Ohm experimentally established the relation among electric current, resistance, voltage in an electric circuit. He found out that the current passing through a conductor varies directly to the voltage applied at its ends, and inversely to the resistance of the conductor. Ohm’s Law may be applied to the whole circuit or to a particular part of a circuit. Review A simple circuit consisting of battery, resistors, and current or flowing charges could be compared to the flow of blood in the circulatory system. Two types of circuit Series circuit - is one that contains more than one piece of electrical apparatus (or resistor) connected one after another in a single line. Parallel circuit - is one where two or more pieces of electrical apparatus (or resistors) are connected side-by-side so that the current is divided between them.  Thanks! CREDITS: This presentation template was created by Slidesgo, including icons by Flaticon and infographics & images by Freepik Please keep this slide for attribution  Resources Pavico, J. F., Ramos, A. M., slidesgo.com Bayquen, A. V., Silverio, A. A., & Ramos, J. A. (2017). Exploring Life Through Science. Quezon City: Phoenix Publishing House, Inc.