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Presentation transcript:

Copyright © Texas Education Agency, 2013. All rights reserved. Electronics Ohm’s Law Copyright © Texas Education Agency, 2013. All rights reserved.

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 Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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- a historical 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) The scientific units for voltage are joule per coulomb. The scientific units for current are coulombs per second. Copyright © Texas Education Agency, 2013. All rights reserved.

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 Copyright © Texas Education Agency, 2013. All rights reserved.

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 Copyright © Texas Education Agency, 2013. All rights reserved.

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 Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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 Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. The Ohm’s Law Circle Copyright © Texas Education Agency, 2013. All rights reserved.

Using The Ohm’s Law Circle Cover the value you want to solve for The remaining two terms give the equation Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example One Solve for Current Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example One Cover the current symbol Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example One Cover the current symbol Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example One Cover the current symbol Current equals voltage divided by resistance Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Two Solve for Voltage Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Two Cover the voltage symbol Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Two Cover the voltage symbol Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Two Cover the voltage symbol Voltage equals current times resistance Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Three Solve for Resistance Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Three Cover the resistance symbol Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Three Cover the resistance symbol Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Example Three Cover the resistance symbol Resistance equals voltage divided by current Copyright © Texas Education Agency, 2013. All rights reserved.

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 Copyright © Texas Education Agency, 2013. All rights reserved.

One Way To Visualize Ohm’s Law One volt is required to push one amp through one ohm resistance. E = IR Volts = Amperes x Ohms Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Common Metric Values Ohm’s Law uses results in both large and small numbers, so a review of metric prefix values is important. Prefix Symbol Fraction Exponent Decimal Giga G 1,000,000,000 Mega M 1,000,000 kilo k 1,000 - 1 centi c 0.01 milli m 0.001 micro μ 0.000001 nano n 0.000000001 Common resistor values are kilo ohms (kΩ) and Mega ohms (MΩ); common currents are milli amps (mA) and micro amps (μA). Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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. Sometimes problems are given as a description similar to this example. Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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 = ? Another way electrical information is given is simply by telling the values like the summary will show on a later slide. Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem One Next, look at the Ohm’s Law Circle V = 12 v R = 150 Ω I = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem One Cover what you are solving for V = 12 v R = 150 Ω I = ? Students should start memorizing the three forms of Ohm’s Law so eventually they will no longer need the circle. Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem One Cover what you are solving for V = 12 v R = 150 Ω I = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem One Cover what you are solving for V = 12 v R = 150 Ω I = ? I = 0.08 A Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Summary of Problem One or I = 80 mA Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem Two You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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 = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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 = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Summary of Problem 2 V = 9 v R = 360 Ω I = ? or I = 25 mA Copyright © Texas Education Agency, 2013. All rights reserved.

Practice Problem Three You have a circuit with a resistance of 900 Ω and a current of 30 mA Copyright © Texas Education Agency, 2013. All rights reserved.

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 = ? Copyright © Texas Education Agency, 2013. All rights reserved.

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 = ? Copyright © Texas Education Agency, 2013. All rights reserved.

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 = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Summary of Problem Three I = 30 mA V = ? or V = 27 v Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem Four I = 59 mA V = 19 v R = ? Most problems will be given as electrical values. Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem Four I = 59 mA V = 19 v R = ? Use the Ohm’s Law Circle, and cover the unknown. Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem Four I = 59 mA V = 19 v R = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. Practice Problem Four I = 59 mA V = 19 v R = ? Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved.

Copyright © Texas Education Agency, 2013. All rights reserved. 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! Copyright © Texas Education Agency, 2013. All rights reserved.