# Current, Resistance, Power

## Current

Definition, with example of calculating the drift velocity current for a copper wire.

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## Ohm's Law

Statement of Ohm's Law with definitions of conductivity, resistance, and resistivity.

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## Ohm's Law for Insulators and Conductors

Comparison of the properties of good conductors and good insulators.

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• Watch {}video clip from Lecture 9 (13:14 - 17:13)

## Ohm's Law and Temperature

Explanation that temperature can cause Ohm's Law to break down. Includes a demonstration of Ohm's Law holding for one resistor and not for another.

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• Watch {}video clip from Lecture 9 (17:13 - 23:09)

## Demonstration: Breakdown of Ohm's Law

Ohm's Law failing to hold for a light bulb with a resistance that varies with temperature.

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• Watch {}video clip from Lecture 9 (23:09 - 27:10)

## Resistors in Series and in Parallel

Definition and comparison of values for resistance, current, and voltage.

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• Watch {}video clip from Lecture 9 (27:10 - 32:38)

## Demonstration: Increasing the Conductivity of Air

Using a candle to increase the conductivity of air near an electroscope.

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• Watch {}video clip from Lecture 9 (32:38 - 36:53)

## Demonstration: Increasing the Conductivity of Water

Using salt to increase the conductivity of water and light a bulb.

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• Watch {}video clip from Lecture 9 (36:53 - 43:08)

Calculation of resistance between body and Earth through a pair of shoes, including a demonstration that this resistance is not high enough to keep charge from flowing.

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• Watch {}video clip from Lecture 9 (43:08 - 49:16)

## Power Supply

Definition and explanation of how a battery works, with examples.

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• Watch {}video clip from Lecture 10 (0:00 - 7:16)

## Batteries in Circuits

Symbol for a battery in a circuit diagram, definition of electromotive force and internal resistance.

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• Watch {}video clip from Lecture 10 (7:16 - 10:50)

## Demonstration: Batteries in Series

Connecting two batteries in series to demonstrate that the electromotive force doubles.

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• Watch {}video clip from Lecture 10 (10:50 - 15:20)

## Power

Derivation of the equation for power P=IV, including definition of Watts as unit of power.

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## Power in a Resistor

Finding the power consumed by a resistor, with examples including light bulbs, heaters, and the human body.

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## Power in a Battery

Finding the power supplied by a battery, with a demonstration of a 9 V battery being shorted out.

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## Demonstration: Shorting a Car Battery

Showing the large current and power supplied by a car battery when it is shorted out.

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• Watch {}video clip from Lecture 10 (28:30 - 31:18)

## Ohm's Law and Kirchhoff's Rules

Finding currents and power in a circuit of batteries and resistors.

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• Watch {}video clip from Lecture 12 (32:47 - 44:14)

## High Voltage Power Lines

Discussion of the advantages of transporting electric energy at high voltages to minimize power loss. Calculation of the maximum voltage possible without causing corona discharge, including a slide of corona discharge on a power line during a storm.

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• Watch {}video clip from Lecture 14 (20:39 - 32:58)

## Current in DC Circuits

Definition of current and current density; microscopic and macroscopic Ohm's Law.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Circuit Conventions

Circuit element symbols; sign conventions; drawing resistors and capacitors.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Equivalent Resistance

Rules governing resistors in series and parallel; how to calculate equivalent resistance in each.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Kirchoff's Circuit Rules

Illustration of Kirchoff's Circuit Rules and method for solving a circuit; includes discussion of internal resistance in batteries.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Measuring Voltage and Current

How to measure voltage, current, and resistance in a circuit.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Electromotive Force

Definition from E-field; car batteries; direction of current flow.

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## More on Solving Circuits

Using Kirchhoff's rules to solve complex circuits; internal resistance and power dissipation.

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## Current and Current Density

Definition of macroscopic current and microscopic current density.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Ohm's Law, Resistance, and Resitivity

Derivation of macroscopic Ohm's Law (V = IR) from microscopic; introduction of resistance, resistivity and conductivity, including temperature effect on resistivity.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Typical Values of Resistivity

A table of values for resistivity and conductivity of several materials.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Resistance of a Cable

Given the dimensions and resistivity of a wire, determine its resistance. Solution is included after problem.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Drift Velocity in Sea Water

Find the average drift velocity for ions in a tube of sea water when a voltage is applied across its length. Solution is included after problem.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Resistance of a Hollow Cylinder

Determine the resistance of a hollow cylinder between the ends and between the inside and outside. Solution is included after problem.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Conceptual Questions on Resistance and Power

Discuss the dependence of resistance on dimensions and temperature, and the dependence of power dissipation on resistance.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Current of a Whirling Charge

A conceptual question about current density of a charged sphere spun in a circle.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Ohm's Law for a Radiant Heater

Given the power and operating voltage of a radiant heater, find the current, resistance and output of the heater.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Drift Speed of Electrons in Copper Wire

How long does it take for an individual electron to travel from a car battery to the starter motor?

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Current Sheets

Describes the concept of a current sheet and explores the calculation of current density per unit length using a Van de Graaff belt example.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Resistance of a Drawn Out Wire

How does the resistance of a wire change if it is drawn out so that its length is increased?

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Ohm's Law for a Lightbulb

Given the power and operating voltage of a lightbulb, find the current, resistance and electricity consumption of the bulb.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Resistivity and Resistance

Identify how the resistance of a conductor depends on its length and area.

• 8.02 Physics II: Electricity and Magnetism, Spring 2007
Prof. John Belcher, Dr. Peter Dourmashkin, Prof. Robert Redwine, Prof. Bruce Knuteson, Prof. Gunther Roland, Prof. Bolek Wyslouch, Dr. Brian Wecht, Prof. Eric Katsavounidis, Prof. Robert Simcoe, Prof. Joseph Formaggio, Andy Neely, Matthew Strafuss, Prof. Eric Hudson, Dr. Sen-Ben Liao

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## Voltage in Power Lines

5-part power problem; finding resistance, power, voltage conditions, and Lorentz force in power lines.

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## 3-Resistor Circuit

5-part problem; determining which bulbs in a circuit are lit when various switches are closed and which are brightest.

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## Bulbs in a Circuit

Determining relative brightness of light bulbs in a resistor circuit.

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