Section 1: Current and Circuits
Electric current is the flow of electric charges.
K
What I Know
W
What I Want to Find Out
L
What I Learned
Chapter Objectives
-Describe the basic properties of electric current and solve problems relating
current, charge and time
-Calculate resistance, current and potential difference by using the definition
of resistance
-Distinguish between ohmic and non-ohmic materials
-Differentiate between direct current and alternating current
-Relate electric power to the rate at which E.E. is converted to other forms of
energy.
-Predict if AC or DC is used over long distances.
-Analyze how resistance is used to protect devices.
Essential Questions
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What is electric current?
How does energy change in electric circuits?
What is Ohm’s law?
How are power, current, potential difference, and resistance mathematically
related?
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Current and Circuits
Vocabulary
Review
New
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electric potential difference
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electric current
conventional current
battery
electric circuit
ampere
resistance
resistor
parallel connection
series connection
Current and Circuits
Starter Activity
What makes
these
appliances to
work?
Resistance and Ohm’s Law
Ohms law state that that the current through a conductor between two
points is directly proportional to the voltage across the two points.
Introducing the constant of proportionality, the resistance,[1] one arrives at
the usual mathematical equation that describes this relationship I= V/R
Resistance and Ohm’s Law
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The property determining how much current will flow is called
resistance.
Resistance is measured by placing a potential difference
across a conductor and dividing the voltage by the current.
The resistance (R) is defined as the ratio of electric potential
difference (ΔV) to the current (I ).
Resistance
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R 
ΔV
I
The resistance of a conductor is measured in ohms (Ω).
One ohm (1 Ω) is the resistance permitting an electric charge of
1 A to flow when a potential difference of 1 V is applied across
the resistance.
There are two ways to control the current in a circuit.
Because I = Δ V/R, I can be changed by varying V, R, or both.
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Current and Circuits
Ways of Controlling current:
Ohmic and Non -ohmic Material
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A device having constant resistance independent of the
potential difference is said to obey Ohm’s law and called ohmic
material.
• Most metallic conductors obey Ohm’s law, at least over a
limited range of voltages.
• A device having variable resistance independent of the
potential difference donot obey Ohm’s law and called Non
ohmic material.
• Transistors and diodes are important electronic components
that do not obey Ohm’s law.
A resistor is a device designed to have a specific resistance.
• Resistors may be made of graphite, semiconductors, or
wires that are long and thin.
A variable resistor, called a potentiometer, can be used to
control the current in circuits or parts of circuits.
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Current and Circuits
Ohmic and non ohmic material
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Electric Current
Factors on which Resistance Depends:
Resistance and Ohm’s Law
Use with Example Problem 2.
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Problem
A 9.0-V battery is connected to a 15-kΩ
resistor. What is the current in this
circuit?
Response
SKETCH AND ANALYZE THE PROBLEM
• Sketch the situation.
• List the knowns and unknowns.
KNOWN
UNKNOWN
∆V = 9.0 V
I=?
R = 15 kΩ
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SOLVE FOR THE UNKNOWN
• Use the relationship among current,
potential difference, and resistance.
I 
ΔV
9.0 V

 0.60 mA
R
15 k
EVALUATE THE ANSWER
• A 0.60-mA current is reasonable for a
9-V battery.
Current and Circuits
Practice problems Pg. No. 607
Practice problems Pg. No. 607
Resistivity & Resistor
Ways of Controlling current:
Review
Essential Questions
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•
•
•
What is electric current?
How does energy change in electric circuits?
What is Ohm’s law?
How are power, current, potential difference, and
resistance mathematically related?
Vocabulary
•
•
•
electric current
conventional current
battery
Copyright © McGraw-Hill Education
•
•
•
electric circuit
ampere
resistance
•
•
•
resistor
parallel connection
series connection
Current and Circuits