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**E1 – Electrical Fundamentals**

# 1 - Atoms and Electrons, Ohm’s Law, and Resistance

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**Atoms Nucleus: the center Electrons Made up of neutrons and protons**

Neutral particles Neither positive nor negative Protons Positively charged particles Electrons Negatively charged particles Orbit around the nucleus 8+ 8n 1 Oxygen atom © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Molecules Atoms can combine to form molecules**

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**8 protons 8 neutrons 8 electrons**

Molecules 1 Hydrogen atom 1 proton 1 electron 1 Hydrogen atom 1 proton 1 electron 1+ 1+ 1 Molecule of Water 1+ 1+ 8+ 8n 8+ 8n 2 Hydrogen + 1 Oxygen = 1 Oxygen atom 8 protons 8 neutrons 8 electrons H2O © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Positive and Negative Charges**

Balanced charge: electrons equal protons Unbalanced charge: allows electrons to flow Negative charge: more electrons than protons Positive charge: less electrons than protons © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Balanced Charge 10 Protons and 10 Electrons “Neutral” 1+ 8+ 8n**

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Positively Charged Molecule**

1+ 8+ 8n 10 Protons and 9 Electrons “Positive” © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Negatively Charged Molecule**

1+ 8+ 8n 10 Protons and 11 Electrons “Negative” © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Conductors Free electrons easily leave their orbits**

Materials with free electrons are conductors Copper atoms have a free electron © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Copper Atom Nucleus of neutrons and protons 29 electrons**

Valence or ‘free’ electron © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Current flow in a Conductor**

Free electrons can be forced to move from atom to atom by: Friction – Static electricity Chemical – Batteries Magnetic (induction) - Generator © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Current flow through copper**

Voltage knocked electron free Copper is a good conductor Empty space attracts free electron © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**OHM’s Law 1 volt will push 1 amp through 1 ohm of resistance**

Electromotive force = Intensity x Resistance E = I x R E = IR Electromotive force (E) = Volts Intensity (I) = Amps Resistance (R) = Resistance in Ohms (Ω) Note: E = I x R can also be expressed as Volts = Amps x Resistance © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Using Ohm’s Law Equation**

E = I x R (Volts = Amps x Resistance) Solving for I, divide R into E: E R = I, or E/R = I Solving for R, divide I into E: E I = R, or E/I = R © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Intro to the Math Behind Ohm’s Law**

You may divide both sides of an equation by any number (except 0.) 50 x 2 = 20 x 5 100 = 20 x 5 5 5 20 = 20 x 5 5 20 = 20 © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**The Math Behind OHM’s Law #1**

E = I x R For example: 10 volts = (2 amps) x (5 ohms) Solve for E: Solve for volts: E = I x R volts = 10 2 x 5 Solve for I: Solve for amps: E = I x R R R 2 10 = amps x 5 5 5 Solve for R: Solve for ohms: E = I I I x R 10 5 = 2 2 2 x ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**The Math Behind OHM’s Law #2**

E = I x R For example: 10 volts = (2 amps) x (5 ohms) Solve for E: Solve for volts: E = I x R volts = 10 2 x 5 Solve for I: Solve for amps: E = I x R 10 2 = amps x 5 Solve for R: Solve for ohms: E = I x R 10 5 = 2 x ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Ohm’s Law Example 1: E = IR Solve for E (voltage): E = 5 amps x 24 Ω**

What is the voltage supplied to the following circuit? R = 24 Ω I = 5 amps E = ? V E = IR Solve for E (voltage): E = 5 amps x 24 Ω E = 5 x 24 E = 120 volts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Ohm’s Law Example 2: E = IR Solve for I (intensity in amps): E R = I**

What is the current (intensity in amps) in the following circuit? R = 10 Ω I = ? amps E = 120 V E = IR Solve for I (intensity in amps): E R = I 120 v 10 Ω = ? amps 120 10 = 12 amps © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Ohm’s Law Example 3: E = IR Solve for R (Resistance in ohms):**

What is the resistance (ohms) of the load below? R = ? Ohms Ω I = .83 amps E = 120 V E = IR Solve for R (Resistance in ohms): E I = R 120 v .83 amps = ? Ω 120 .83 = 145 Ω © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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Ohm’s Law Disc Using a “disc” is another way to solve the Ohm’s Law equation © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**E = Electromotive Force**

OHM’s Law Disc E = Electromotive Force (Volts) E I R I = Intensity (Amps) R = Resistance (OHMS Ω) © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**E R I R= E I I= E R E=I x R To find Voltage To find Resistance**

OHM’s Law Disc To find Voltage To find Resistance To find Current E R I R= E I I= E R E=I x R © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Reviewing OHM’s Law Disc**

E = Electromotive Force (Volts) I = Intensity (Amps) R = Resistance (OHMs Ω) E R I To find Voltage E = I x R E R I To find Current I = E R I To find Resistance R = © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Calculating Electrical Power**

“Power is the rate at which work is done.” Power = Intensity x Electromotive force P = IE Power (watts) = Amps x Volts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Power (watts) = Amps x Volts Power = Intensity x Electromotive force **

Ohm’s Law Example 4: Example 4: What is the power consumption of an electric circuit using 15 amperes and 120 volts? Power (watts) = Amps x Volts Power = Intensity x Electromotive force P = IE P = 15 amps x 120 volts P = 15 x 120 P = 1800 Watts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Power (watts) = Amps x Volts Power = Intensity x Electromotive force **

Example 5: What is the current of an electric heater rated at 4800 watts on 240 volts? Ohm’s Law Example 5: Power (watts) = Amps x Volts Power = Intensity x Electromotive force P = IE solve for I P E = I 4800 watts 240 volts = I (amps) 4800 240 = 20 Amps © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Power = Amps2(squared) x Ohms Power = Intensity2 x Resistance P = I2R **

Ohm’s Law Example 6: Example 6: What is the power of an electric circuit with 5 amps current and 10 ohms resistance? Power = Amps2(squared) x Ohms Power = Intensity2 x Resistance P = I2R P = 52 amps x 10 ohms P = 52 x 10 P = 25 x 10 P = 250 Watts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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Ohm’s Law Wheel All applications of Ohm’s Law formulas can be represented as the spokes of a wheel. © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**E is Electromotive force in Volts**

Ohms Law Wheel E2 R E R P is Power in Watts I is Intensity in Amps I2 R P E IE P R P E I R E .I PR P .I E2 P P I2 IR E is Electromotive force in Volts R is Resistance in Ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Resistance & Loads Resistance: Loads:**

Opposition to electron flow in the circuit Measured in ohms (Ω) Loads: Must have some resistance Provide a path for electron flow © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Compare resistance to crossing a river**

Resistance is the open space between the shores Cars represent electrons Bridges represent loads Without bridges there is no way the cars can cross This is known as “infinite” resistance © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Infinite Resistance Infinite Resistance**

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**A load is added The load provides a path for electrons**

There is still high resistance to flow But it is no longer infinite resistance © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**But there is still High Resistance**

A small load provides a path for some of the electrons But there is still High Resistance © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**More load is added Less resistance More electron flow**

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**The resistance is lower**

Lower resistance means more electrons, or current flow. The resistance is lower © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Low or no resistance can be bad**

The lower the resistance, The higher the electron flow If the current flow is out of control, The circuit is overloaded © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**If resistance is too low, electron flow will be too high. OVERLOAD**

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**Resistance, Watts, and Amps**

Load resistance affects amps and watts The lower a load’s resistance, The higher it’s amps and watts © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**How Resistance affects Amps and Watts**

(Note: approximate values in an alternating current 120v circuit) OPEN L1 N Infinite Resistance ∞ Ohms (R) No Watts (P) No Amps (I) 1500 Ohms .08 A 10 W 150 Ohms .8 A 100 W 15 Ohms 1000 W 8 A BOOM High Watts & High Amps Circuit Breaker Trips 0 Ohms © 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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**END OF Atoms and Electrons, Ohm’s Law, and Resistance**

© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0

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