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Chapter 17 Current and Resistance 1. Electric current 2. Drift speed 3. Current and voltage measurement 4. Ohm’s law 5. Resistivity 6. Superconductivity 7. Electric energy and power

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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?

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Current and Drift Speed Current defined in terms of charge carrier and drift speed Isolated conductor Conductor with electric field Drift speed and circuits

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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?

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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?

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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?

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Georg Simon Ohm 1787 – 1854 Formulated the concept of resistance Discovered the proportionality between current and voltages

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Ohm’s Law Statement of ohm’s law What is an Ohmic device? What is non- Ohmic device? Examples

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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.

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Resistance & Resistivity What is resistivity? Resistivity of metals? See table 17.1 Resistance and Temperature

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Example 1. The heating element in an electric stove contains a wire of 1.1m and cross-sectional area 3.1x10 -6 m 2 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.

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Superconductors What are superconductors? Why superconductors?

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Energy Transfer in the Circuit What is grounding? Energy considerations

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Electrical Energy and Power What is power? How do I calculate it? What are the SI units? What is kilowatt-hour? Conversion factor

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Example 1. In the flashlight the current is 0.40A and the voltage is 3.0 V. Find a) The power delivered to the bulb b) The electrical energy dissipated in the bulb in 5.5 minutes of operation.

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Electrical Activity in the Heart Normal

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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

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RESISTANCE – OHM’S LAW Lesson 5. Resistance The amount of current flow in a circuit, and the amount of energy transferred to any useful device, depends.

RESISTANCE – OHM’S LAW Lesson 5. Resistance The amount of current flow in a circuit, and the amount of energy transferred to any useful device, depends.

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