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## Electronics

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**Electronics**Ohm’s Law**Presentation Overview**• Terms and definitions • Letters and terms used in Ohm’s Law • Ohm’s Law • Use of the Ohm’s Law circle • Applications of Ohm’s Law**Terms and Definitions**• Voltage- electrical potential; an electrical pressure created by the buildup of charge; causes charged particles to move • Volt- unit of voltage; Symbol= V • Electromotive force- ahistorical term used to describe voltage; Symbol= E • (No longer relevant, the definition of force is something that causes a mass to accelerate, and voltage or EMF does not fit that definition). E is now commonly used as a symbol for electric field strength. • Current- the flow or movement of electrons • Ampere- unit of current; Symbol= I • Resistance- opposition to current flow • Ohm- unit of resistance; Symbol= Ω(Greek symbol Omega)**Terms and Definitions (continued)**• Energy- the fundamental ability to do work • Joule- unit of energy; Symbol= J • Electrical Power- the rate of electrical energy used in a circuit; calculated by multiplying current times voltage, or P = V • I • Watt- unit of measurement for power; a watt is one joule per second (J/s); Symbol= W • Ohm’s Law- a formula describing the mathematical relationship between voltage, current, and resistance; one of the most commonly used equations in all of science**Terms and Definitions (cont)**• Directly proportional- having a constant ratio; a situation where one variable moves in the same direction as another variable when other conditions are constant • Inversely proportional- having a constant but inverse ratio; a situation where one variable moves in the opposite direction from another variable when other conditions remain constant • Example- current doubles when voltage is doubled if resistance is held constant; thus, voltage and current are directly proportional • Example- with a constant voltage, current decreases when resistance increases; thus, current and resistance are inversely proportional**Review of Letters and Terms used in Ohm’s Law**• I – Electrical current in amperes • R – Resistance in ohms • V – Represents voltage in volts • A – Represents amperes • Ω– Represents ohms • E – Electromotive force (emf) in volts, sometimes used as an alternate symbol for voltage**Ohm’s Law**• A mathematical formula typically expressed as, (Read as “current equals voltage divided by resistance.”) • This formula can be rearranged in two more ways: and**Using The Ohm’s Law Circle**• Cover the value you want to solve for • The remaining two terms give the equation**Example One**• Solve for Current**Example One**• Cover the current symbol**Example One**• Cover the current symbol**Example One**• Cover the current symbol Current equals voltage divided by resistance**Example Two**• Solve for Voltage**Example Two**• Cover the voltage symbol**Example Two**• Cover the voltage symbol**Example Two**• Cover the voltage symbol Voltage equals current times resistance**Example Three**• Solve for Resistance**Example Three**• Cover the resistance symbol**Example Three**• Cover the resistance symbol**Example Three**• Cover the resistance symbol Resistance equals voltage divided by current**Three Forms of Ohm’s Law**1. Calculating circuit resistance Example: R = V / I 2. Calculating circuit amperage Example: I = V / R 3. Calculating circuit voltage Example: V = IR**One Way To Visualize Ohm’s Law**Ohm’s Law One volt is required to push one amp through one ohm resistance. E = IR Volts = Amperes x Ohms**Common Metric Values**Ohm’s Law uses results in both large and small numbers, so a review of metric prefix values is important.**Practice Problem One**• You have a circuit with a source voltage of 12 V DC and a circuit resistance of 150 Ω. Solve for the unknown value using Ohm’s Law.**Practice Problem One**• You have a circuit with a source voltage of 12 V DC and a circuit resistance of 150 Ω. Solve for the unknown value using Ohm’s Law. • To solve, first write down all values V = 12 v R = 150 Ω I = ?**Practice Problem One**• Next, look at the Ohm’s Law Circle V = 12 v R = 150 Ω I = ?**Practice Problem One**• Cover what you are solving for V = 12 v R = 150 Ω I = ?**Practice Problem One**• Cover what you are solving for V = 12 v R = 150 Ω I = ?**Practice Problem One**• Cover what you are solving for V = 12 v R = 150 Ω I = ? I = 0.08 A**Summary of Problem One**or I = 80 mA**Practice Problem Two**• You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω**Practice Problem Two**• You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω • Write down all of the values V = 9 v R = 360 Ω I = ?**Practice Problem Two**• You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω • Write down all of the values V = 9 v R = 360 Ω I = ?**Summary of Problem 2**V = 9 v R = 360 Ω I = ? or I = 25 mA**Practice Problem Three**• You have a circuit with a resistance of 900 Ω and a current of 30 mA**Practice Problem Three**• You have a circuit with a resistance of 900 Ω and a current of 30 mA R = 900 Ω I = 30 mA V = ?**Practice Problem Three**• You have a circuit with a resistance of 900 Ω and a current of 30 mA R = 900 Ω I = 30 mA V = ?**Practice Problem Three**• You have a circuit with a resistance of 900 Ω and a current of 30 mA R = 900 Ω I = 30 mA V = ?**Summary of Problem Three**R = 900 Ω I = 30 mA V = ? or V = 27 v**Practice Problem Four**I = 59 mA V = 19 v R = ?**Practice Problem Four**I = 59 mA V = 19 v R = ?**Practice Problem Four**I = 59 mA V = 19 v R = ?**Practice Problem Four**I = 59 mA V = 19 v R = ?**Presentation Summary**• Terms and definitions • Letters and terms used in Ohm’s Law • Ohm’s Law • Ohm’s law in circular expression • Use of Ohm’s Law Let’s do some problems!