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Basic Electrical Theory: Understanding Ohm’s Law Copyright © Texas Education Agency, 2011. All rights reserved.

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2 Introduction What is Ohm ’ s Law? Why is ohms law important? The Electrical Components of Ohm ’ s Law 1. Electromotive Force 2. Current 3. Resistance 4. Power Ohm ’ s Law Formulas Using The Ohm ’ s Law Chart to calculate electrical circuits.

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Copyright © Texas Education Agency, 2011. All rights reserved.3 Terms to Remember The Source can be any source of electrical energy. In practice, there are three general possibilities: it can be a battery, an electrical generator, or some sort of electronic power supply. The Load is any device or circuit powered by electricity. It can be as simple as a light bulb or as complex as a modern high-speed computer. (Path) a wire or pathway which will allow electron to flow throughout a circuit. Electricity can be described as the flow of charged particles. If the particles accumulate on an object, we term this static electricity. (Direct Current) An electrical current that travels in one direction and used within the computer's electronic circuits. (Alternating Current) The common form of electricity from power plant to home/office. Its direction is reversed 60 times per second. Circuit is a conducting path for electrons.

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Copyright © Texas Education Agency, 2011. All rights reserved.4 What is Ohm ’ s Law? Ohm's Law states that, at constant temperature, the electric current flowing in a conducting material is directly proportional to the applied voltage, and inversely proportional to the Resistance. Why is Ohms Law important? Ohm’s Law is the relationship between power, voltage, current and resistance. These are the very basic electrical units we work with. The principles apply to alternating current (ac), direct current (dc), or radio frequency (rf).

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Copyright © Texas Education Agency, 2011. All rights reserved.5 The Electrical Components of Ohm ’ s Law Voltage The electrical "pressure" that causes free electrons to travel through an electrical circuit. Also known as electromotive force (emf). It is measured in volts. Resistance That characteristic of a medium which opposes the flow of electrical current through itself. Resistance is measured in ohms. Power The amount of current times the voltage level at a given point measured in wattage or watts. Current The amount of electrical charge (the number of free electrons) moving past a given point in an electrical circuit per unit of time. Current is measured in amperes

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Copyright © Texas Education Agency, 2011. All rights reserved.6 Ohm’s Law Formulas This is Ohm's law, where E = Volts; I = current in amperes and R = resistance in ohms. Ohm’s Law expresses the relationship between the current (I), the voltage (E), and the resistance (R) in a circuit. Ohm’s Law can be expressed in three different ways, and can be applied to the entire circuit or to any part of a circuit. When any two factors are known, the third unknown factor can be calculated from Ohm’s Law.

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Copyright © Texas Education Agency, 2011. All rights reserved.7 Characteristics Of Ohm’s Law Voltage: Difference of potential, electromotive force, ability to do work. Unit of measure Volt Symbol E or V (This symbol will be used in the Ohms Law Formula) Compares to Pressure in a gas or liquid system. Current: Flow of electrons Unit of measure Ampere Symbol I (This symbol will be used in the Ohms Law Formula) Compares to The flow of gas or liquid in a piping system. Resistance: Opposition to current flow Unit of measure Ohm often seen as the Greek letter Omega Symbol R (This symbol will be used in the Ohms Law Formula) Compares to Orifice effect or the size restriction of inside pipe Diameter.

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Copyright © Texas Education Agency, 2011. All rights reserved.8 Finding Voltage Ohm’s Law Formula for Finding Voltage (E) (I) (R) Voltage = Current x Resistance To find Voltage Multiply the Current times the Resistance. E=I x R Using the Magic Circle Cover the E to see the mathematical relationship between Voltage and Current

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Copyright © Texas Education Agency, 2011. All rights reserved.9 Finding Current Ohm’s Law Formula for Finding Current (I) (E) Current= Voltage ———— (R) Resistance To find Current Divide the Voltage by the Resistance E I = — R Using the Magic Circle Cover the I to see the mathematical relationship between Voltage and Resistance

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Copyright © Texas Education Agency, 2011. All rights reserved.10 Finding Resistance Ohm’s Law Formula for Finding Resistance (R) (E) Resistance= Voltage ——— (I) Current To find Resistance Divide the Voltage by the Current E R = — I Using the Magic Circle Cover the R to see the mathematical relationship between Voltage and Current

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Copyright © Texas Education Agency, 2011. All rights reserved.11 In this algebraic expression, voltage (E) is equal to current (I) multiplied by resistance (R). Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively: Let's see how these equations might work to help us analyze simple circuits: In the above circuit, 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 very easy to apply Ohm's Law. 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.

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Copyright © Texas Education Agency, 2011. All rights reserved.12 In this first example, we will calculate the amount of current (I) in a circuit, given values of voltage (E) and resistance (R): What is the amount of current (I) in this circuit?

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Copyright © Texas Education Agency, 2011. All rights reserved.13 In this second example, we will calculate the amount of resistance (R) in a circuit, given values of voltage (E) and current (I): What is the amount of resistance (R) offered by the lamp?

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Copyright © Texas Education Agency, 2011. All rights reserved.14 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?

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Copyright © Texas Education Agency, 2011. All rights reserved.15 Ohm's Law is a very simple and useful tool for analyzing electric circuits. It is used extensively in the study of electricity and electronics. Remember When any two factors are known, the third unknown factor can be calculated from Ohm’s Law.

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Copyright © Texas Education Agency, 2011. All rights reserved.16 Ohm's Law is a very simple and useful tool for analyzing electric circuits. It is used extensively in the study of electricity and electronics. Remember When any two factors are known, the third unknown factor can be calculated from Ohm’s Law. REVIEW: Voltage measured in volts, symbolized by the letters "E" or "V". Current measured in amps, symbolized by the letter "I". Resistance measured in ohms, symbolized by the letter "R". Ohm's Law: E = IR ; I = E/R ; R = E/I

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