Properties and Effects of Electric Currents
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### Lecture Description

A - The Oersted Frame: In 1820 Hans Christian Oersted - a Dane -
made an observation that stirred an avalanche in physical thought. He discovered that a current-bearing conductor gives rise to a magnetic field. We show this classic experiment. Faraday - an Englishman - heard of this great adventure and made a note in his notebook: "Make magnetism produce electricity". In 1831 Faraday did just this with his famous discovery of electromagnetic induction.

B - Metals are good electrical conductors - this we know. But how about liquids and solutions? We show a solution of copper sulphate with two lead electrodes. We "drive" a current through this solution from a storage battery and soon we see a marvelous thing: One of the lead plates has some COPPER ON IT. We thus show the conductivity in an electrolyte and the deposition of copper by electrolysis. This is copper plating.

C - How about conductivity in a "hot dog"? Sure enough - we impale a "cold" dog on two spikes - connect the system to the house line -110 volts AC - and we cook the dog! The conductivity is possible because of the salt in the meat which makes it a good conductor.

D - We connect a Cu wire to a dry-cell in a circular loop and present the wire to some iron filings. The filings gather tightly at the wire. Is the wire magnetized? No. It is not magnetized but the current-bearing wire produces a magnetic field which is strongest nearby the wire.

E - If two adjacent conductors carry a current the conductors may be pushed apart or pushed together depending on the direction of the current in them. So we suggest a demonstration using a coil known as Roget's Spiral. We avoid doing this experiment because it leads to the vaporization of mercury - which is very bad to breathe!

F - The Electromagnetic Gun: A coil of wire of HEAVY wire and few turns — this makes its Ohmic resistance low - is wound on an aluminum tube. In the tube resides an iron bar. We make connection for an instant to a 6-volt battery. The coil - now carrying a current -magnetizes the bar - draws the bar IN - AND - if we now open the circuit at the right instant the bar keeps going as a projectile. As can be seen - if the circuit is not closed and opened at critical times the weapon will not work!

G - We "short" a 6-volt storage battery by putting a Cu wire across its terminals. The current drawn momentarily may be as high as several hundred amperes.The heat developed burns the wire. What really happens is this: The wire is evaporated!

So - in these adventures - we see that an electric current can produce mechanical effects - magnetic effects - heating effects - chemical effects - optical effects - and so on. And we must not lose sight of Oersted and Faraday and scores of others whose genius made it all possible.

### Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.