Download Electricity

Name
Date
Electricity
Section 2 Electric Current
Scan Use the checklist below to preview Section 2 of your book.
• Read all section titles.
• Read all bold words.
• Read all charts and graphs.
• Look at all the pictures and read their captions.
• Think about what you already know about electricity.
Write two facts you discovered about electric currents as you
scanned the section.
1. Accept all reasonable responses.
2.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Review
Vocabulary Use the term pressure in a scientific sentence.
SI
International System of Units – the improved universally accepted
version of the metric system that is based on multiples of ten
and includes the meter (m), liter (L), and kilogram (kg)
New
Vocabulary Define the following key terms.
electric current
voltage difference
electric circuit
resistance
Ohm’s law
the rate of movement of electric charges in a single direction
related to the force that causes electric charges to flow
a closed path that electric current follows
the tendency for a material to oppose the flow of electrons
the current in a circuit equals the voltage difference divided by
the resistance
Academic
Vocabulary Use a dictionary to define terminate.
terminate
coming to an end or capable of ending
Electricity
71
Name
Date
Section 2 Electric Current
Current and
Voltage
Difference
I found this information
on page
.
SE, p. 179
RE, p. 97
(continued)
Create a drawing of an electric circuit that has a battery
powering a digital clock. Show the direction of electron flow, and
describe the movement of the electrons in the circuit.
Accept all reasonable
Accept all reasonable responses.
responses. Electrons flow
12:00
away from the negative
Electron flow
terminal and toward the
positive terminal of the
Battery
battery.
I found this information
on page
.
SE, p. 180
RE, pp. 97–98
Compare dry-cell batteries to wet-cell batteries. Describe the
components of each type of battery. In your own words, explain
how it works. Accept all reasonable responses.
Battery Type
How It Works
Dry-cell
two electrodes
(carbon rod, zinc
container)
electrolyte
(conducting
chemicals in a
moist paste)
When the two terminals
are connected in a
circuit, the zinc and the
electrolyte react.
Electrons move to make
the terminal connected
to the carbon rod
positive. Electrons build
up on the zinc cylinder,
making its terminal
negative. The voltage
difference between the
terminals makes current
flow.
Wet-cell
two connected
plates made of
different metals in a
conducting solution
Chemical reactions
transfer electrons from
one plate to the other
plate, making one
terminal positive and the
other terminal negative.
Challenge advanced
students by asking
them to name different
types of batteries now
available, and to
predict how their
composition might
differ from standard
zinc batteries.
72 Electricity
Components
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Batteries
Name
Date
Section 2 Electric Current
Resistance
Summarize the source of resistance in a material.
I found this information
on page
.
Accept all reasonable responses. As electrons flow through a
I found this information
on page
.
Organize the factors that affect the electrical resistance of a
material. Write each word in one of the boxes below.
SE, p. 181
RE, p. 99
SE, p. 181
RE, p. 99
Ohm’s Law
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
(continued)
I found this information
on page
.
SE, p. 182
RE, p. 100
Students can work
with partners to derive
the formulas for
Ohm’s law.
material, they bump into the atoms that make up the material.
hotter
cooler
longer
shorter
thicker
thinner
More Resistance
Less Resistance
hotter, longer, thinner
cooler, shorter, thicker
Define three equations that come from Ohm’s law.
Unknown Value
Current
Known Values
Voltage difference
Resistance
Equation
Resistance
Voltage difference
Current
V
R ! ""
I
Voltage difference
Current
Resistance
V ! IR
V
I ! ""
R
S YNTHESIZE I T
Electricians use different thickness of copper wire when
they create the electrical circuits in a home. Use your knowledge of resistance to
explain why an electrician would choose a thicker wire for a circuit that will provide
power to a high-current appliance.
Accept all reasonable responses. A thicker wire would have less resistance than a thinner
wire. It will generate less heat than a thinner wire when conducting a high current.
Electricity
73