Electrical Principles and
Technology
Final Exam Review
Key Concepts
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Forms of energy
Energy transformation
Generation of electrical energy
Electric charge and current
Circuits
Electrical energy storage
Energy transmission
Measures and units of electrical energy
Electrical resistance and Ohm’s law
Renewable and non-renewable energy
Charges
• Excess electrons on an object create a negative
charge.
• A shortage of electrons creates a positive charge.
• Static electricity: a charge produced by
rubbing or touching objects together
• Electric discharge: the rebalancing of an
unbalanced charge, felt as a shock or seen as a
spark
Laws of Charge
• The Laws of Charge state that
▫ Unlike charges attract
▫ Like charges repel
▫ Charged objects attract uncharged (neutral)
objects
Conductors and Insulators
• Conductors: materials that allow electric
charge to move freely
▫ Most metals are conductors
• Insulators: any material in which the charge
stats on the spot where the object was rubbed;
materials that prevent charge from moving
freely
▫ Most non-metals are insulators
Circuits
• The basic parts of all electric circuits are:
▫
▫
▫
▫
A source of electric energy
Conductors
A load
A control device
• A series circuit has one current path.
• A parallel circuit has more than one path along
which current can flow.
Units!!!
• Quantity of charge is measured in coulombs (C)
• Current (I) is measured in amperes (A)
• Voltage/potential difference (V) is a measure
of the energy of a standard unit of charge, and is
measured in volts (V).
• Resistance (R) is measured in Ohms (Ω)
Resistance and Ohm’s Law
• Resistance is the property of substances that
hinders charge motion and converts electric
energy into heat.
• Resistance is defined as the ratio of voltage to
current (Ohm’s Law):
V
R=
I
Energy
• The energy consumed by a device is the
product of the power drawn, and the amount of
time (in seconds!!) over which it is drawn.
• Energy is always measured in joules.
E=P×t
Energy Converters
• Thermocouples convert thermal energy to
electric energy.
• Piezoelectric materials generate a small voltage
when the pressure on them changes.
• Photovoltaic (solar) cells convert light energy to
electric energy.
Batteries
• Battery: a combination of cells, either wet or
dry.
▫ Chemical reactions between the electrodes and
electrolyte produce a voltage.
• Electrodes: the two metals in a voltaic or
electrochemical cell
• Electrolytes: a substance that conducts an
electric current, and in which electrodes are
placed
Current Flow
• Direct current (DC) flows in only one direction.
• Alternating current (AC) reverses direction
periodically.
Motors and Generators
• Electric generators convert mechanical energy to
electric energy.
• Electric motors convert electric energy to
mechanical energy.
• Their operation is based on the relationship
between magnetism and electricity.
Generators
Alternating Current
Direct Current
Transmission of Electricity
• The power grid generates and distributes AC
electricity using transformers to change voltage
for efficient power transmission.
• Transformers: used to “step up” the voltage
for efficient transmission of current over long
distances
Electricity in Homes
• In homes, electric current travels through an
electric meter and a service panel to branch
circuits.
• Circuit breakers or fuses in the service panel cut
off excessive current before wiring can overheat.
Power
• Electric power is the product of voltage and
current.
P=I×V
• Power measures the quantity of energy transfer
each second.
▫ The unit for power is the watt (W).
Efficiency
• All electric devices convert some input energy
into waste heat, so they are not perfectly
efficient.
output
efficiency =
× 100%
input
Electric Energy Production
• Most of Canada’s electric energy is generated
using dams, thermo-electric plants that burn
fossil fuels, and nuclear reactions.
• All methods of producing electricity affect the
environment. Renewable sources of electric
energy include biomass fuels and solar, wind,
tidal and geothermal energy.
What to Expect on the PAT
• From this unit:
▫ 10 multiple choice questions
▫ 1 numerical response question
▫ 3 “knowledge” questions
▫ 8 “skills” questions
Do I Get a Formula Sheet?
Examples of Knowledge Questions
When clothes are removed from
a clothes dryer, sparks can be
seen as the clothes are separated.
These sparks are a result of
Which of the following
modifications to an
electromagnet will increase its
strength?
A.
B.
C.
D.
A. Using a larger iron core
B. Using fewer coils of copper
wire
C. Increasing the resistance of
the iron core
D. Decreasing the current
passing through the coils of
copper wire
Current electricity
An electrical discharge
A buildup of neutral atoms
Anti-static sheets absorbing
neutral charges
Examples of Skills Questions
Which of the following wet cells
would product the highest
voltage?
Joe watches television for 6.00
hours (21 600 seconds). The
input power rating of his
television is 200 W. The
electrical energy consumed by
any electrical device can be
calculated using the following
formula.
The total electrical energy
consumed by Joe’s television is
A.
B.
C.
D.
33.3 J
108 J
1.20 kJ
4.32 MJ
More Skills Questions
The resistance in the circuit
shown above is
A.
B.
C.
D.
2Ω
3Ω
4Ω
6Ω