Transcript Chapter 17

Chapter 17
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Current and Resistance
Electric current
Drift speed
Current and voltage measurement
Ohm’s law
Resistivity
Superconductivity
Electric energy and power
Electric Current
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What is an electric current?
How do I calculate current?
What are the SI units?
What is the direction of current in
a circuit?
What is conventional current?
Current and Drift Speed
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Current defined in
terms of charge
carrier and drift
speed
Isolated conductor
Conductor with
electric field
Drift speed and
circuits
Example
1.
The battery pack of a pocket
calculator has a voltage of 3.0 V
and delivers a current of 0.17 mA.
In one hour of operation,
a)
b)
How much charge flows in the
circuit?
How much energy does the battery
deliver to the calculator circuit?
Meters in a Circuit
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What is
How do
What is
How do
an ammeter?
I connect it in a circuit?
a voltmeter?
I connect it in a circuit?
Resistance
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What is a resistor?
What is the relationship between
voltage and current in a circuit?
What is electrical resistance?
What the SI units of resistance?
What is Ohm’s law?
Georg Simon Ohm
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1787 – 1854
Formulated the
concept of
resistance
Discovered the
proportionality
between current
and voltages
Ohm’s Law
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Statement of
ohm’s law
What is an Ohmic
device?
What is nonOhmic device?
Examples
Example
1.
A filament in a light bulb is
resistor in the form of a thin wire.
The wire becomes hot enough to
emit light because of the current
in it. A flashlight uses two 1.5 V
batteries to provide a current of
0.40 A in the filament. Determine
the resistance of the glowing
filament.
Resistance & Resistivity
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What is resistivity?
Resistivity of metals?
See table 17.1
Resistance and Temperature
Example
1.
The heating element in an electric
stove contains a wire of 1.1m and
cross-sectional area 3.1x10-6 m2
through which electric charge flows.
The wire becomes hot in response to
the flowing charge. The resistivity of
the material is 6.8x10-3 °C-1 at 320 °C.
Determine the resistance of the heater
wire at an operating temperature of
420 °C.
Superconductors
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What are
superconductors?
Why
superconductors?
Energy Transfer in the
Circuit
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What is
grounding?
Energy
considerations
Electrical Energy and
Power
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What is power?
How do I calculate it?
What are the SI units?
What is kilowatt-hour?
Conversion factor
Example
1.
In the flashlight the current is
0.40A and the voltage is 3.0 V.
Find
a)
b)
The power delivered to the bulb
The electrical energy dissipated in
the bulb in 5.5 minutes of operation.
Electrical Activity in the
Heart
Normal
Implanted Cardioverter
Defibrillator (ICD)
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Devices that can
monitor, record and
logically process
heart signals
Then supply different
corrective signals to
hearts that are not
beating correctly