1. E1 – Electrical Fundamentals
# 1 - Atoms and Electrons, Ohm’s Law, and Resistance

2. 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
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3. Molecules Atoms can combine to form molecules
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4. 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
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5. 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
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6. Balanced Charge 10 Protons and 10 Electrons “Neutral” 1+ 8+ 8n
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7. Positively Charged Molecule1+ 8+ 8n
10 Protons and 9 Electrons
“Positive”
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8. Negatively Charged Molecule1+ 8+ 8n
10 Protons and 11 Electrons
“Negative”
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9. Conductors Free electrons easily leave their orbits
Materials with free electrons are conductors
Copper atoms have a free electron
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10. Copper Atom Nucleus of neutrons and protons 29 electrons
Valence or ‘free’ electron
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11. 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
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12. Current flow through copper
Voltage knocked electron free
Copper is a good conductor
Empty space attracts free electron
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13. 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
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14. 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
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15. 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
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16. 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
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17. 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
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18. 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
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19. 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
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20. 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
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21. Ohm’s Law Disc
Using a “disc” is another way to solve the Ohm’s Law equation
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22. E = Electromotive Force
OHM’s Law Disc
E = Electromotive Force
(Volts) E I R
I = Intensity
(Amps)
R = Resistance
(OHMS Ω)
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23. 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
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24. 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 =
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25. Calculating Electrical Power
“Power is the rate at which work is done.”
Power = Intensity x Electromotive force
P = IE
Power (watts) = Amps x Volts
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26. 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
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27. 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
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28. 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
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29. Ohm’s Law Wheel
All applications of Ohm’s Law formulas can be represented as the spokes of a wheel.
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30. 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
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31. 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
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32. 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
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33. Infinite Resistance Infinite Resistance
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34. 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
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35. But there is still High Resistance
A small load provides a path for some of the electrons
But there
is still
High Resistance
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36. More load is added Less resistance More electron flow
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37. The resistance is lower
Lower resistance means more electrons, or current flow.
The
resistance
is lower
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38. 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
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39. If resistance is too low, electron flow will be too high. OVERLOAD
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40. Resistance, Watts, and Amps
Load resistance affects amps and watts
The lower a load’s resistance,
The higher it’s amps and watts
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41. 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
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42. END OF Atoms and Electrons, Ohm’s Law, and Resistance
© 2005 Refrigeration Training Services - E1#1 Atoms,Electron,Ohms Law,Resistance v1.0