Conceptual Physics Alive: Electrostatics, Electric Current, Magnetism & E&M Induction
Master teacher Paul Hewitt teaches non-computational Conceptual Physics. Observe Hewitt teach in a classroom with real students, using engaging demonstrations and artwork.
DVD Includes 3 Episodes:
Episode 1: Electrostatics: Electrostatic charging is demonstrated in a variety of ways--with a rubber rod, cat's fur, an electrophorus, a Whimshurst electrostatic generator, and a Van De Graaff generator. Lightning rods, charging by induction, and charge polarization are also discussed. Segment length: 35 minutes
Episode 2: Electric Current: Concepts in electric current and examples of Ohm's law are discussed. Series and parallel circuits are demonstrated using a car battery that has extended terminals. Segment length: 30 minutes
Episode 3: Magnetism and E&M Induction: Electromagnets, motors, generators, and magnetic levitation are examined, using numerous examples and demonstrations. Segment length: 41 minutes
• Hewitt begins with review of atomic structure.
• Fundamental rule of electricity; opposite charges attract, like charges repel.
• Atoms are compared to the solar system.
• Net charge and why hydrogen atoms combine to form molecules.
• Chemical bonding.
• Coulomb's law compared to Newton's law of gravitation.
• Demonstration of charging of rubber rod on eat's fur.
• Benjamin Franklin's role in electricity.
• Conservation of charge.
• Demonstration of suspended Ping Pong ball interacting with negative and positive rods.
• Demonstration of charge polarization.
• Demonstration of electrophorus.
• Demonstration of Whimshurst electrostatic generator.
• Lightning rods.
• Lightning storms.
• Benjamin Franklin and lightning rods.
• Demonstration of Van de Graaff generator (because of high humidity in Hawaii, not very effective).
• Electric field.
Next-time Question: What is the reason for the lamp glowing when held horizontally near the charged dome of the Van de Graaff generator, and not glowing when held vertically? [When held horizontally, one end was closer to the dome, which means one end was in a region of greater voltage. So a voltage difference was established across the ends of the tube and a current was produced. When the lamp was held vertically, both ends were equidistant and therefore at the same voltage. No voltage difference means no current, as the next lesson will show.]
Electric Current includes:
• Begins by reviewing the Van de Graaff generator and the surrounding electric field.
• Voltage defined.
• Energy transferred by the generator compared to the energy transferred by a common household circuit.
• Analogy to heat and temperature.
• Current and voltage difference.
• Water flow analogy of electric current.
• Demonstration of single lamp attached to car battery.
• Hewitt discusses childhood experiences with electricity.
• Birds on high-tension wires.
• Boston MTA story.
• Cherry picker story.
• 2nd Boston MTA story.
• Ohm's law defined.
• Water flow analogy.
• DC and AC defined.
• Washing machine analogy.
• Amount of electrons that flow in an AC circuit (none).
• Demonstration of series circuit with battery, and many questions.
• Demonstration of parallel circuit with battery, and many questions.
Next-Time Questions: As more and more resistors are connected to a parallel circuit, does the overall resistance of the circuit become more, less, or stay the same? [The resistance becomes more, because there are more paths available to the current; or more resistors are like making the resistive wire thicker, and resistance is less.]
Magnetism and E&M Induction includes:
• Hewitt begins by picking up paper clips with a magnet.
• Magnetic compass shown.
• Demonstration of Orsted's discovery.
• Exploratorium view of circular shape of magnetic field about a current carrying wire.
• Magnetic field about bar magnet.
• Demonstration of electromagnet
• Residual magnetism
• Magnetic domains.
• Demonstration of current carrying wire jumping in a magnetic field.
• Electric motor.
• Electric meter.
• Electric motor demonstration.
• Demonstration of electromagnetic induction.
• Faraday's law.
• Motor effect and generator effect.
• Demonstration of motor and generator effect.
• Generator demonstration.
• Demonstration of electromagnetic repulsion.
• Demonstration of electromagnetic levitation.
• Ted Brattstrom demonstrates compass motion in a current carrying coil.
1) Why did the ring pop up on the electromagnet? [The ring encompassed a changing magnetic field that induced voltage in it, and thereby current, that made the ring into a small electromagnet, which was magnetically repelled by the large electromagnet.]
2) Why is a generator harder to turn when it lights a lamp? [Current is made to flow when the lamp is lit, and this current is in the coils of wire in the magnetic field of the generator. Work must be done to move a current carrying wire in a magnetic field, even though the current is induced by that same magnetic field. So more current causes more 'electromagnetic repulsion' that makes the crank harder to turn.]