Chapter 17
Section 3 Current and
Resistance
Objectives
• Recognize what causes charges to flow through a
circuit/conductor
• Describe the basic properties of electric current, and
solve problems relating current, charge, and time.
• Distinguish between the drift speed of a charge
carrier and the average speed of the charge carrier
between collisions.
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Chapter 17
Section 3 Current and
Resistance
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Chapter 17
Section 3 Current and
Resistance
What are the requirements for a charge
to move through a conductor?
What charges are the ones that flow
through the conductor?
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Chapter 17
Section 3 Current and
Resistance
Electronic Current and Conventional Current:
Electronic Current
• Is described as the flow of
electrons.
• Electrons flow from the
negative terminal to the
positive.
Conventional Current
• Conventional current or
simply current, behaves as
if positive charge carriers
cause current flow.
• Conventional current flows
from the positive terminal
to the negative.
A charge Carrier is a particle that
carries an electric charge
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Chapter 17
Section 3 Current and
Resistance
Electronic Current and Conventional
Current:
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Chapter 17
Section 3 Current and
Resistance
Current and Charge Movement
• If 7200 cars pass a toll gate “SALIK” in 1 hour, what
is the rate of flow of cars through that gate each
second.
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Chapter 17
Section 3 Current and
Resistance
Current and Charge Movement
• Now, if Electric current is defined as the rate at
which electric charges pass through a given area,
write a formula to calculate the electric current.
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Chapter 17
Section 3 Current and
Resistance
Current and Charge Movement
• Electric current is the rate at which electric charges
pass through a given area.
I
electric current =
Q
t
charge passing through a given area
time interval
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Chapter 17
Section 3 Current and
Resistance
What do you think??!
How does the current change if the number of
charge carriers increases?
How does the current change if the time interval
during which a given number of charge carriers
pass the cross-sectional area increases?
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Chapter 17
Section 3 Current and
Resistance
Sample Problem C Page 597:
The current in a light bulb is 0.835 A. How
long does it take for a total charge of 1.67 C to
pass through the filament of the bulb?
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Chapter 17
Section 3 Current and
Resistance
Practice Problems Page 597:
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Chapter 17
Section 3 Current and
Resistance
Extra Practice:
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Chapter 17
Section 3 Current and
Resistance
Extra Practice:
Describe the relationship between
electric potential difference and
electric current
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Chapter 17
Section 3 Current and
Resistance
Drift Velocity
• Drift velocity is the net
velocity of a charge
carrier moving in an
electric field.
• When an electron moves
through a conductor,
collisions with the
vibrating metal atoms of
the conductor force the
electron to change its
direction constantly.
Change in direction Velocity change.
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Drift speeds are relatively
small because of the many
collisions that occur when
an electron moves through
a conductor.
Chapter 17
Section 3 Current and
Resistance
What Causes Charges to Flow
through a Conductor?
What opposes the flow of charges
through a conductor?
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