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Transmission of Electricity through the Power Grid
1. Looking at the diagram on page 318, write down the sequence of where the
electricity originates until it eventually reaches your home. Power generation
station – step up transformer – wire towers – to sub station – wire towers –
distribution station – wire towers – step-down transformer – to your house.
2. What produces alternating currents for use in homes and industry? Large
electric generators in power stations.
3. What do transformers do? Explain the difference between the 'step up'
transformers and the 'step down' types of transformers. Step up transformers
increase the voltage for efficient transmission over long distances. Step down
transformers decrease voltage for use in homes and factories.
From the Grid into Your Home
4. What does a meter do? It records the total electric energy supplied to electric
devices that are operation in the house.
5. What is the role of a circuit breaker? The main breaker acts as a switch and
safety device that can cut off all power coming into the home.
6. For older homes, instead of a circuit breaker, they have a fuse box. What is
the purpose of a fuse box? A fuse contains a metallic conductor that melts when
excessive current heats it up. This opens the circuit until the fuse is replaced.
7. Explain how the lower part of the service panel works. It contains additional
circuit breakers or fuses for each branch circuit in your home.
8. In electrical wiring in the house, explain and point out the color of the following
types of wires:
a) neutral wire – white
b) hot wire – black
c) ground wire – either bare or covered with green
Home Wiring
9. Why do we follow an electrical code? To make sure any wiring job meets a
set of standards.
Digital Devices
10. The four basic circuit elements are: conductors, loads, switches and electrical
source. In a circuit board inside a calculator, identify each of these four basic
circuit elements are found. Conductors may be thin traces of copper instead of
wires. Loads are resistors and lamps. Switches, there can be thousands or
millions of tiny electronic switches. Electrical source is household power or
batteries.
11. Explain what transistors are. The electronic switches in modern digital
devices are transistors, solid-state components that can be turned on and off by
electric signals.
Measuring Electric Power
12. Define power. Energy per unit time.
13. What are the two the mathematical equation that defines power? (be sure to
include the units) Power (in watts) = Energy (in joules) / Time (in seconds)
Power (in watts) = Current (in amps) x Voltage (in volts)
Practice Problems Answers pg 324
1. P = IV
P = (10 A)(120 V) = 1200 W
1200 W of power would be needed to operate the
hair dryer.
2. P = IV
P = (2 A)(120 V) = 240 W
The television uses 240 W of power.
3. V = P/I
V = 900 W/ 7.5 A = 120 V
The microwave requires a voltage of 120 V.
4. P = IV
P = (0.5 A)(3.0 V) = 1.5 W
The wattage of the bulb would be 1.5 W.
Practice Problem Answers pg 325
1. (a) Power = 700W = 0.7 kW
time = (24 h/day) (30 days) = 720 h
Power Consumption in 30 days = (0.7 kW) 
( 720 h) = 504 kWh
(b) Cost of Power = ($0.11 / kWh) X (504 kWh) =
$55.44
2. (a) 100 W = 0.10 kW; 42 bulbs = 4.2 kW
Time used = 5 h/day 30 days = 150 h
Power consumption (kWh) = 4.2 kW 150 h =
630 kWh
The light bulbs would consume 630 kWh of
power in 30 days.
(b) Cost to operate the lights = 630 kWh 3 $0.11 /
kWh = $69.30
It would cost $69.30 to operate the lights.
(c) (0.052 kW 42) 150 h = 327.6 kWh
(630 kWh – 327.6 kWh) $0.11/kWh = $33.26
The homeowner would save $33.26 per month.
3. (a) W = I V
W = 120 V 2.5 A = 300 W or 0.3 kW
Bob’s stereo needs 300 W of power to operate.
300W = .3kWh
.2*150 = 45kWh