1
Q
- What is the basic particle of negative charge?
A
- The electron is the basic particle of negative charge.
2
Q
- Define atom.
A
- An atom is the smallest particle of an element that retains the unique characteristics of the
element.
3
Q
- What does an atom consist of?
A
- An atom is a positively charged nucleus surrounded by orbiting electrons.
4
Q
- Define atomic number.
A
- Atomic number is the number of protons in a nucleus.
5
Q
- Do all elements have the same types of atoms?
A
- No, each element has a different type of atom.
6
Q
- What is a free electron?
A
- A free electron is an outer-shell electron that has drifted away from the parent atom.
7
Q
- What is a shell in the atomic structure?
A
- Shells are energy bands in which electrons orbit the nucleus of an atom.
8
Q
- Name two conductive materials.
A
- Copper and silver
9
Q
- What is a Coulomb?
- What is the formula to find it?
- What is the value of 1 Coulomb?
A
- the SI unit of electric charge, equal to the quantity of electricity conveyed in one second by a current of one ampere. Q = Total Charge.
- Q = (number of electrons /
6.25 X 10^18 electrons/C) - 6.25 x 10^18
10
Q
How many coulombs of charge do 93.8 X 10^16 electrons represent?
A
Q = number of electrons / 6.25 * 1018 electrons/C = 93.8 X 10^16 electrons / 6.25 * 10^18 electrons/C = 15 X 10^-2 C = 0.15 C
11
Q
- Define voltage
A
- Voltage is energy per unit charge.
12
Q
- What is the unit of voltage?
A
- The unit of voltage is the volt.
13
Q
- What is the voltage when 24 J of energy are required to move
10 C of charge?
A
- V = W/Q = 24 J>10 C = 2.4 V
14
Q
- List seven sources of voltage.
A
- Battery, fuel cell, power supply, solar cell, generator, thermocouple, and piezoelectric sensors
are voltage sources.
15
Q
- What type of chemical reaction occurs in all batteries and fuel
cells?
A
- Oxidation-reduction reactions
16
Q
- Define current and state its unit.
A
- Current is the rate of fl ow of charge; the unit of current is the ampere (A).
17
Q
- How many electrons make up one coulomb of charge?
A
- There are 6.25 X 10^18 electrons in one coulomb.
18
Q
- What is the current in amperes when 20 C flow past a point in a wire in 4 s?
A
- I = Q/t = 20 C / 4 s = 5 A
19
Q
- Define resistance and name its unit.
A
- Resistance is opposition to current and its unit is the ohm
20
Q
- What are the two main categories of resistors? Briefly explain the difference between them.
A
- Two resistor categories are fixed and variable. The value of a fixed resistor cannot be changed, but that of a variable resistor can.
21
Q
- In the 4-band resistor color code, what does each band represent?
A
- First band: first digit of resistance value.
Second band: second digit of resistance value.
Third band: number of zeros following the 2nd digit.
Fourth band: percent tolerance.
22
Q
- Determine the resistance and percent tolerance for each of the
following color codes:
(a) yellow, violet, red, gold
(b) blue, red, orange, silver
(c) brown, gray, black, gold
(d) red, red, blue, red, green
A
- (a) Yellow, violet, red, gold = 4700 +/- 5%
(b) Blue, red, orange, silver = 62,000 +/- 10%
(c) Brown, gray, black, gold = 18 +/- 5%
(d) Red, red, blue, red, green = 22.6 k +/- 0.5%
23
Q
- What resistance value is indicated by each alphanumeric label:
(a) 33R
(b) 5K6
(c) 900
(d) 6M8
A
- (a) 33R = 33 Ohm
(b) 5K6 = 5.6 k Ohm
(c) 900 = 900 Ohm
(d) 6M8 = 6.8 M Ohm
24
Q
- What is the basic difference between a rheostat and a
potentiometer?
A
- A rheostat has two terminals; a potentiometer has three terminals.
25
7. Name three resistance sensors and the physical quantity that
affects their resistance.
7. Thermistor—temperature; photoconductor cell—light; strain gauge—force.
26
1. What are the basic elements of an electric circuit?
1. A basic electric circuit consists of source, load, and current path between source and load.
27
2. Define open circuit.
2. An open circuit is one that has no path for current.
28
3. Define closed circuit.
3. A closed circuit is one that has a complete path for current.
29
4. What is the resistance of an open switch? Ideally, what is the resistance of a closed switch?
4. R = (infinite); R = 0 Ohm
30
5. What is the purpose of a fuse?
5. A fuse protects a circuit against excessive current.
31
6. What is the difference between a fuse and a circuit breaker?
6. A fuse must be replaced once blown. A circuit breaker can be reset once tripped.
32
7. Which wire is larger in diameter, AWG #3 or AWG #22?
7. AWG #3 is larger than AWG #22.
33
8. What is ground in an electric circuit?
8. Ground is the reference point with zero voltage with respect to other points.
34
1. Name the multi meter functions for measuring
(a) current
(b) voltage
(c) resistance
1.
(a) Ammeter measures current.
(b) Voltmeter measures voltage.
(c) Ohmmeter measures resistance.
35
4. List two common types of DMM displays, and discuss the
advantages and disadvantages of each.
4. Two types of DMM displays are LED and LCD. The LCD requires little current, but it is difficult to see in low light and is slow to respond. The LED can be seen in the dark, and it responds
quickly; however, it requires much more current than does the LCD.
36
5. Define resolution in a DMM.
5. Resolution is the smallest increment of a quantity that a meter can measure.
37
T/F Quiz
1. The number of neutrons in the nucleus is the atomic number of that element.
2. The unit of charge is the ampere.
3. Energy in a battery is stored in the form of chemical energy.
4. A volt can be defined in terms of energy per charge.
5. In a five-band precision resistor, the fourth band is the tolerance band.
6. A rheostat performs the same function as a potentiometer.
7. A strain gauge changes resistance in response to an applied force.
8. Soldering is never allowed on a splice.
9. All circuits must have a complete path for current.
10. A circular mil is a unit of area.
11. The three basic measurements that can be done by a DMM are voltage, current, and power.
12. To measure current with a meter, the meter should be placed in series.
1. F
2. F
3. T
4. T
5. F
6. F
7. T
8. F
9. T
10. T
11. F
12. T
38
Self Test
1. A neutral atom with an atomic number of three has how many electrons?
(a) 1 (b) 3 (c) none (d) depends on the type of atom
2. Electron orbits are called
(a) shells (b) nuclei (c) waves (d) valences
3. Materials in which current cannot be established are called
(a) filters (b) conductors (c) insulators (d) semiconductors
4. When placed close together, a positively charged material and a negatively charged material will
(a) repel (b) become neutral (c) attract (d) exchange charges
5. The charge on a single electron is
(a) 6.25 X 10^ −18 C (b) 1.6 X 10^−19 C (c) 1.6 X 10^−19 J (d) 3.14 X 10^−6 C
6. Potential difference is another term for
(a) energy (b) voltage (c) distance of an electron from the nucleus (d) charge
7. The unit of energy is the
(a) watt (b) coulomb (c) joule (d) volt
8. Which one of the following is not a type of energy source?
(a) battery (b) solar cell (c) generator (d) potentiometer
9. Which one of the following is the byproduct of a hydrogen fuel cell?
(a) oxygen (b) carbon dioxide (c) hydrochloric acid (d) water
10. Which one of the following is generally not a possible condition in an electric circuit?
(a) voltage and no current
(b) current and no voltage
(c) voltage and current
(d) no voltage and no current
11. Electrical current is defined as
(a) free electrons
(c) the energy required to move electrons
(b) the rate of flow of free electrons
(d) the charge on free electrons
12. There is no current in a circuit when
(a) a series switch is closed
(b) a series switch is open
(c) there is no source voltage
(d) both (a) and (c)
(e) both (b) and (c)
13. The primary purpose of a resistor is to
(a) increase current
(b) limit current
(c) fixed resistors
(d) circuit breakers
14. Potentiometers and rheostats are types of
(a) voltage sources
(b) variable resistors
(c) produce heat
(d) resist current change
15. The current in a given circuit is not to exceed 22 A. Which value of fuse is best?
(a) 10 A
(b) 25 A
(c) 20 A
(d) a fuse is not necessary
1. (b)
2. (a)
3. (c)
4. (c)
5. (b)
6. (b)
7. (c)
8. (d)
9. (d)
10. (b)
11. (b)
12. (e)
13. (b)
14. (b)
15. (c)
39
1. Briefly state Ohm’s law in words.
1. Ohm’s law states that current varies directly with voltage and inversely with resistance.
40
2. Write the Ohm’s law formula for calculating current.
2. I = V/R
41
3. Write the Ohm’s law formula for calculating voltage.
3. V = IR
42
4. Write the Ohm’s law formula for calculating resistance.
R = V/I
43
5. If the voltage across a resistor is tripled, does the current
increase or decrease? By how much?
5. The Current increases; three times when V is tripled
44
6. There is a fixed voltage across a variable resistor, and you
measure a current of 10 mA. If you double the resistance, how
much current will you measure?
6. Doubling R cuts I in half to 5 mA.
45
7. What happens to the current in a linear circuit where both the
voltage and the resistance are doubled?
7. No change in I if V and R are doubled.
46
1. V = 10 V and R = 4.7 Ohms Find I
1. I = 10 V / 4.7 Ohms = 2.13 A
47
2. If a 4.7 Mohms resistor has 20 kV across it, how much current is there?
2. I = 20kV / 4.7 Mohms = 4.26 mA
48
3. How much current will 10 kV across a 2 kohms resistance produce?
3. I = 10 kV / 2 kohms = 5 A
49
4. I = 1 A and R = 10 ohms Find V
4. V = 1 A x 10 Ohms = 10V
50
5. What voltage do you need to produce 3 mA of current in a 3 kohms resistance?
5. V = 3 mA x 3 kohms = 9 V
51
6. A battery produces 2 A of current through a 6 ohms resistive load. What is the battery voltage?
6. V = 2 A x 6 ohms = 12 V
52
7. V = 10 V and I = 2 A. Find R.
7. R = 10 V / 2 A = 5 Ohms
53
8. In a stereo amplifier circuit there is a resistor across which
you measure 25 V, and your ammeter indicates 50 mA of
current through the resistor. What is the resistor’s value in
kilohms? In ohms?
8. R = 25 V / 50 mA = .5 Kohms = 500 Ohms
54
1. Define power.
1. Power is the rate at which energy is used.
55
2. Write the formula for power in terms of energy and time.
P = W/t
56
3. Define watt.
3. Watt is the unit of power. One watt is the power when 1 J of energy is used in 1 s.
57
4. Express each of the following values of power in the most
appropriate units:
(a) 68,000 W
(b) 0.005 W
(c) 0.000025 W
(a) 68,000 W = 68 kW
(b) 0.005 W = 5 mW
(c) 0.000025 = 25 microW
58
5. If you use 100 W of power for 10 h, how much energy (in
kilowatt-hours) have you used?
5. (100W)(10 h) = 1 kWh
59
6. Convert 2000 W to kilowatts.
6. 2000 W = 2 kWh
60
7. How much does it cost to run a heater (1322 W) for 24 hours
if energy cost is 11¢ per kilowatt-hour?
7. (1.322 kW)(24 h) = 31.73 kWh; (0.11 $/kWh)(31.73 kWh) = $3.49
61
1. Assume a car window defroster is connected to 13.0 V and has
a current of 12 A. What power is dissipated in the defroster?
1. P = IV = (12 A)(13 V) = 156 W
62
2. If there is a current of 5 A through a 47 Ohms resistor, what is the
power dissipated?
2. P = (5 A)^2 x (47 Ohms) = 1175 W
63
3. Many oscilloscopes have a 50 Ohms input position that places a
2 W, 50 Ohms resistor between the input and ground. What is the
maximum voltage that could be applied to the input before
exceeding the power rating of this resistor?
3. V = Sqrt(PR) = Sqrt(2 W x 50 Ohms) = 10 V
64
4. Assume a car seat heater has an internal resistance of 3.0 Ohms
If the battery voltage is 13.4 V, what power is dissipated by
the heater when it is on?
4. P = V^2 / R = 13.4^2 V / 3 Ohms = 60 W
65
5. How much power does a 2.2 kohms resistor with 8 V across it
produce?
5. P = (8 V)^2 / 2.2 Kohms = 29.1 mW
66
6. What is the resistance of a 55 W bulb that draws 0.5 A?
6. R = 55 W / (.5 A)^2 = 220 Ohms
67
1. Name two important parameters associated with a resistor.
1. Two resistor parameters are resistance and power rating.
68
2. How does the physical size of a resistor determine the amount
of power that it can handle?
2. A larger resistor physical size dissipates more energy.
69
3. List the standard power ratings of metal-film resistors.
3. Standard ratings of metal-film resistors are 0.125 W, 0.25 W, 0.5 W, and 1 W.
70
4. A resistor must handle 0.3 W. What standard size metal-film
resistor should be used to dissipate the energy properly?
4. At least a 0.5 W rating to handle 0.3 W
71
5. What is the maximum voltage that can be applied to a ¼ W,
100 Ohms resistor if the power rating is not to be exceeded?
5. 5 V
72
1. What is the basic reason for energy conversion in a resistor?
1. Energy conversion in a resistor is caused by collisions of free electrons with the atoms in the
material.
73
2. What is a voltage drop?
2. Voltage drop is a decrease in voltage across a resistor due to a loss of energy.
74
3. What is the polarity of a voltage drop in relation to current
direction?
3. Voltage drop is negative to positive in the direction of current.
75
1. When a loading device draws an increased amount of current
from a power supply, does this change represent a greater or a
smaller load on the supply?
1. An increased amount of current represents a greater load.
76
2. A power supply produces an output voltage of 10 V. If the
supply provides 0.5 A to a load, what is the power output?
2. Pout = 10 V x .5 A = 5 W
77
3. If a battery has an ampere-hour rating of 100 Ah, how long
can it provide 5 A to a load?
3. 100 Ah / 5 A = 20h
78
4. If the battery in Question 3 is a 12 V device, what is its power
output for the specified value of current?
4. Pout = 12 V / 5 A = 60 W
79
5. A power supply used in the lab operates with an input power
of 1 W. It can provide an output power of 750 mW. What is
its efficiency?
5. Efficiency = (750 mW / 1000mW) x 100% = 75%
80
1. Name the three steps in the APM (analysis, planning, and measurement) approach to troubleshooting.
1. Analysis, Planning, and Measuring
81
2. Explain the basic idea of the half-splitting technique.
2. Half-splitting identifies the fault by successively isolating half of the remaining circuit.
82
3. Why are voltages easier to measure than currents in a circuit?
3. Voltage is measured across a component. Current is measured in series with the component.
83
T/F Quiz
1. if the total resistance of a circuit increases, current decreases.
2. Ohm’s law for finding resistance is R= I > V .
3. When milliamps and kilohms are multiplied together, the result is volts.
4. if a 10 kohms resistor is connected to a 10 V source, the current in the resistor will be 1 A.
5. The kilowatt-hour is a unit of power.
6. One watt is equal to one joule per second.
7. The power rating of a resistor should always be less than the required power dissipation in the
circuit.
8. Within limits, a regulated power supply can automatically keep the output voltage constant
even if the load changes.
9. A power supply that has a negative output voltage absorbs power from the load.
10. When analyzing a circuit problem, you should consider the conditions under which it failed.
1. T
2. F
3. T
4. F
5. F
6. T
7. F
8. T
9. F
10. T
84
Self Test
1. Ohm’s law states that
(a) current equals voltage times resistance
(b) voltage equals current times resistance
(c) resistance equals current divided by voltage
(d) voltage equals current squared times resistance
2. When the voltage across a resistor is doubled, the current will
(a) triple (b) halve (c) double (d) not change
3. When 10 V are applied across a 20 resistor, the current is
(a) 10 A (b) 0.5 A (c) 200 A (d) 2 A
4. When there are 10 mA of current through a 1.0 k resistor, the voltage across the resistor is
(a) 100 V (b) 0.1 V (c) 10 kV (d) 10 V
5. If 20 V are applied across a resistor and there are 6.06 mA of current, the resistance is
(a) 3.3 kohms (b) 33 kohms (c) 330 ohms (d) 3.03 kohms
6. A current of 250 microA through a 4.7 kohms resistor produces a voltage drop of
(a) 53.2 V (b) 1.175 mV (c) 18.8 V (d) 1.175 V
7. A resistance of 2.2 M is connected across a 1 kV source. The resulting current is approximately
(a) 2.2 mA (b) 455 microA (c) 45.5 microA (d) 0.455 A
8. Power can be defined as
(a) energy
(b) heat
(c) the rate at which energy is used
(d) the time required to use energy
9. For 10 V and 50 mA, the power is
(a) 500 mW
(b) 0.5 W
(c) 500,000 microW
(d) answers (a), (b), and (c)
10. When the current through a 10 kohms resistor is 10 mA, the power is
(a) 1 W
(b) 10 W
(c) 100 mW
(d) 1 mW
11. A 2.2 kohms resistor dissipates 0.5 W. The current is
(a) 15.1 mA
(b) 227 microA
(c) 1.1 mA
(d) 4.4 mA
12. A 330 Ohms resistor dissipates 2 W. The voltage is
(a) 2.57 V
(b) 660 V
(c) 6.6 V
(d) 25.7 V
13. The power rating of a resistor that is to handle up to 1.1 W should be
(a) 0.25 W (b) 1 W (c) 2 W (d) 5 W
14. A 22 Ohms half-watt resistor and a 220 ohms half-watt resistor are connected across a 10 V source.
Which one(s) will overheat?
(a) 22 (b) 220 (c) both (d) neither
15. When the needle of an analog ohmmeter indicates infinity, the resistor being measured is
(a) overheated (b) shorted (c) open (d) reversed
1. (b)
2. (c)
3. (b)
4. (d)
5. (a)
6. (d)
7. (b)
8. (c)
9. (d)
10. (a)
11. (a)
12. (d)
13. (c)
14. (a)
15. (c)
85
