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Chapter 17
Current and Resistance1. Electric current2. Drift speed3. Current and voltage measurement4. Ohm’s law5. Resistivity6. Superconductivity7. Electric energy and power
Electric Current 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 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) How much charge flows in the circuit?
b) How much energy does the battery deliver to the calculator circuit?
Meters in a Circuit
What is an ammeter? How do I connect it in a circuit? What is a voltmeter? How do I connect it in a circuit?
Resistance 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 1787 – 1854 Formulated the
concept of resistance
Discovered the proportionality between current and voltages
Ohm’s Law Statement of
ohm’s law What is an Ohmic
device? What is non-
Ohmic device? Examples
Example1. 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 What is resistivity? Resistivity of metals? See table 17.1 Resistance and Temperature
Example1. 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 What are
superconductors? Why
superconductors?
Energy Transfer in the Circuit What is
grounding? Energy
considerations
Electrical Energy and Power 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) The power delivered to the bulbb) The electrical energy dissipated in
the bulb in 5.5 minutes of operation.
Electrical Activity in the Heart
Normal
Implanted Cardioverter Defibrillator (ICD)
Devices that can monitor, record and logically process heart signals
Then supply different corrective signals to hearts that are not beating correctly