1. Topics Chapter 2 – Voltage, Current and Resistance Atoms
Electrical Charge
Voltage
Current
Resistance
Basic Circuits

2. What are ATOMS?

3. The two simplest atoms: hydrogen and helium.

4. Energy levels increase as the distance from the nucleus increases.

5. The valence shell
The outer shell is called the valence shell.
Electrons in this shell are involved in chemical reactions and they account for electrical and thermal conductivity in metals.

6. The valence shell
Metals have one, two or three electrons in the valence shell. The atom illustrated here is a sodium atom (Na), with only one electron in its outer shell.
Sodium is highly reactive, and easily gives up its single valence electron. For this reason, it is not used in electrical work.
Non-metals have either complete or nearly compete outer shells, so they make poor electrical conductors (i.e. they are insulators).
Sodium atom

8. A neutral Si atom is shown. There are 4 electrons in the valence shell.
Is Si a conductor, insulator, or semiconductor? 10

9. The valence shell

10. A neutral Si atom is shown. There are 4 electrons in the valence shell.
Is Si a conductor, insulator, or semiconductor?
Semiconductor 12

11. The copper atom

13. Electrical charge
There is a force (F) between electrical charges. Like charges repel; unlike charges attract.
The force is directly proportional to charge.
The force is inversely proportional to square of distance.

14. Electrical charge
Coulomb – The unit of charge
One Coulomb is the total charge possessed by 6.25× electrons.
Total Charge
𝑄= 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 6.25× 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/𝐶

15. Electrical charge
How many coulombs of charge do 88.7× electrons represent?
𝑄= 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 6.25× 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/𝐶
𝑄= 88.7× 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 6.25× 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/𝐶
𝑄=14.91× 10 −3 𝐶= 𝐶

16. Voltage
Force is required to move a charge against the electric field.
When force is applied over a distance, work is done. Work done in moving a charge against the electric field leads to the definition of voltage:
Voltage is the work per charge done against the electric field.

17. The equation for voltage is
V - Volts
W – Energy in joules
Q – Charge in coulombs
One volt is the potential difference (voltage) between two points when one joule of energy is used to move one coulomb of charge from one point to the other.

18. If 135 J of energy are required to move 15C of Charge, what is the voltage?
𝑉= 135𝐽 15𝐶 =9𝑉

19. Symbol for dc voltage sources (battery).
Voltage is responsible for establishing current.

20. Batteries in Parallel
Batteries in Series

21. Batteries
An automobile battery is an example of a multiple cell battery. Like all batteries, the automotive battery does not store charge – it stores chemical energy that can be converted to current when an external path is provided to allow the chemical reaction to proceed.
Rather than saying “charging” a battery, it is more accurate to say “reversing the chemical reaction” in a battery.

22. Fuel cells
A fuel cell is a device that converts chemical energy into dc voltage directly by combining a fuel (usually hydrogen) with an oxidizing
agent (usually oxygen). The hydrogen and oxygen react to form water. The process differs from batteries in that the reactants constantly flow into the cell where they combine and produce electricity.

23. Construction of a basic solar cell.

24. A basic power supply.

25. Electrons flow from negative to positive when a voltage is applied across a conductive or semiconductive material.

26. Current
Current (I in amperes or amps) is the amount of charge (Q in coulombs) that flows past a point in a unit of time (t). The defining equation is:
One coulomb equals the value of electrical charge in ×1018 protons or electrons
One ampere is a number of electrons having a total charge of 1 Coulomb moving through a given cross section in 1 s.
What is the current if 2 C passes a point in 5 s?
0.4 A

27. Current sources are not as common as voltage sources
Symbol

28. the reciprocal of resistance the ease of with which voltage flows.
Conductance
Conductance is:
the reciprocal of resistance
the ease of with which voltage flows.
G – Conductance (S siemens)
R – Resistance (ohms Ω)

29. Resistance
Components designed to have a specific amount of resistance are called resistors.

30. Resistance/resistor symbol.

31. Fixed resistors (Value cannot be changed)

32. Typical fixed resistors

33. Resistance color-code
Resistance value, first three bands:
First band – 1st digit
Second band – 2nd digit
*Third band – Multiplier (number of
zeros following second digit)
Fourth band - tolerance
* For resistance values less than 10 W, the third band is either gold or silver. Gold is for a multiplier of 0.1 and silver is for a multiplier of 0.01.

34. Color-code bands on a 4-band resistor.

35. What is the resistance and tolerance of each of the four-band resistors?
Green, brown, red, gold
5.1 kW ± 5%
820 kW ±10%
47 W ± 10%
1.0 W ± 5%
Gray, red, yellow, silver
Yellow, violet, black, silver
Brown, black, gold,gold

36. Three-digit labeling for a resistor.

37. Alphanumeric Labeling
Two or three digits, and one of the letters R, K, or M are used to identify a resistance value.
The letter is used to indicate the multiplier, and its position is used to indicate decimal point position.
R – multiplier of 1 and no zeros after the digits
K - multiplier of 1000 and 3 zeros after the digits
M - multiplier of 1,000,000 and 6 zeros after the digits

38. Variable resistors include the potentiometer and rheostat.
The center terminal of a variable resistor is connected to the wiper. R
Variable resistor (potentiometer – divides voltage) R
Variable resistor (rheostat – controls current)
To make a potentiometer into a rheostat, one of the outside terminals is connected to the wiper.

39. Potentiometers and construction views.

40. Symbols for resistance devices with sensitivities to temperature, light, and force.

41. A simple electric circuit

43. Switches
Switches are commonly used to control circuits by either mechanical or electronic means.
The throw refers to how many circuits are affected by the movable arm of a switch.
Different from the book
The pole refers to the number of contacts that are available to form a circuit.

44. Normally open Pushbutton
Normally closed Pushbutton

48. Closed and open circuits using a SPST switch for control.

49. SPDT switch controlling two lamps.

50. Mechanical limit switches
Various sizes
Various shapes
Various uses

51. Mechanical limit switches
Micro switches
Small size
Various ranges of uses

52. Mechanical limit switches
Purpose
To detect the presence or absence of an object
Opens or closes a contact

53. Mechanical limit switches4 1 2

54. Mechanical limit switches

55. GAUGING (MODULE #2)

57. Mechanical limit switch in process sequence

58. Mechanical limit switches
What can go wrong
Broken arm
Internal broken contact
Welded contacts
Arc/pitted contacts
Bad/loose connection
Incorrect adjustment
Possible symptoms?
No change in signal
No signal
Continual signal
Intermittent signal

59. Mechanical limit switch
How to check and adjust
Check continuity
Check voltages
Look for changes when switching
Check and readjust as necessary

60. Fuses, circuit breakers and their symbols.

61. WIRE Gauge – Size (AWG or mm)

62. WIRE Gauge – Size (AWG or mm)
In the AWG scale, the smaller the number the larger the wire diameter and the greater the current carrying capacity.

64. Wire resistance
Sometimes, the resistance of wires must be accounted for. The equation for wire resistance is:
where r (rho) = resistivity in CM-W/ft
l = length in feet
A = cross sectional area in circular mils (CM)
What is the resistance of 400 feet of 22 gage copper wire where the area is 642 CM and the resistivity of copper is CM-W/ft and the resistance/1000 feet is W/1000 feet.
By proportion, the resistance of 400 feet is 0.4 x W =
6.46 W
By the equation,
6.46 W

65. Ground. (Reference Point for measuring Potential)
In U.S. this is typically a bare wire or green insulation or green with yellow stripe insulation.
1 – Overvoltage protection – lightning
2 – Voltage Stabilization- Common reference
3 – Safety – What happens if neutral breaks?

66. Simple circuit with ground connections.

67. A basic electric circuit consists of a voltage source a path a load.
The electric circuit
Switch
Battery (2 cells)
Lamp
A basic electric circuit consists of
a voltage source
a path
a load.
An example of a basic circuit is a flashlight, which has each of these plus a control element – the switch.

68. The DMM – Digital Multimeter
Volts - AC
Volts - DC
Ohms
Amperes

69. An analog multimeter is also called a VOM (volt-ohm-milliammeter).
Analog meters
An analog multimeter is also called a VOM (volt-ohm-milliammeter).
No resistance will show as infinite ohms

70. Measuring current
Series Circuit

71. Measuring voltage or voltage drop
Parallel Circuit

72. Measuring resistance

74. Schematic Symbols Review

75. Key Terms Ampere AWG Charge Circuit The unit of electrical current.
(American Wire Gauge) A standardization based on wire diameter.
An electrical property of matter that exists because of an excess or a deficiency of electrons. Charge can be either + or -.
An interconnection of electronic components designed to produce a desired result. A basic circuit consists of a source, a load, and an interconnecting path.

76. Key Terms Conductance Coulomb Current Electron Ground Ohm (W)
The ability of a circuit to allow current. The unit is the siemans (S).
The unit of electrical charge.
The rate of flow of electrical charge.
A basic particle of electrical charge in matter. The electron possesses a negative charge.
The common or reference point in a circuit.
The unit of resistance.

77. Key Terms Potentiometer Resistance Rheostat Siemens Volt Voltage
A three-terminal variable resistor.
The opposition to current. The unit is the ohm (W).
A two-terminal variable resistor.
The unit of conductance.
The unit of voltage or electromotive force.
The amount of energy per charge available to move electrons from one point to another in an electric circuit.

78. Quiz 1. The atomic number is the number of a. protons in the nucleus
b. neutrons in the nucleus
c. protons plus neutrons in the nucleus
d. electrons in the outer shell

79. Quiz 2. Valence electrons are a. in the outer shell
b. involved in chemical reactions
c. relatively loosely bound
d. all of the above

80. Quiz
3. The atomic particle responsible for electrical current in solid metallic conductors is the
a. proton
b. electron
c. neutron
d. all of the above

81. Quiz
4. The symbol for charge is
a. C
b. W
c. Q
d. W

82. Quiz
5. The definition for voltage is a. b. c. d.

83. Quiz 6. A battery stores a. electrons b. protons c. ions
d. chemical energy

84. Quiz 7. The unit of conductance is the a. ohm b. coulomb c. siemen
d. ampere

85. Quiz 10. The circular mil is a unit of a. length b. area c. volume
d. resistance