Introduction To Electricity (1948)

[Music] this is a story about electricity not the whole story but what David Gregor learned when he tried out his new plastic flashlight just then his sister Marilyn came to his room wondering why her comb was giving here so much trouble it seemed to stick to her hair picking up the ends what David heard reminded him of the sound he had often heard during summer thunderstorms and it reminded him of how when he scuffed his feet on the rug and then touched metal a spark jumped these are all examples of what we call static electricity Marilyn tried to wipe off her comb but look it picked up tiny pieces of paper but static electricity doesn't last long enough to do any work to light a bulb we must have a flow of current electricity anyone can make current electricity in a chemical cell say out of zinc and copper when these metals are placed in water and soda we have one form of wet cell with an electric voltmeter David showed her the electricity that is made it's the same kind of electricity that's made in a flashlight cell this is what you might call electricity in a package this flashlight dry cell has a higher voltage than David's little copper zinc cell it has enough to light a tiny one cell flashlight bulb and that's how a flashlight works the electricity flows in a circuit or path from the batteries through the bulb through this metal strip inside and back through the batteries but electricity flows only when the circuit is complete Marilyn wanted to know how to make electricity for the house David said he thought it was made with magnets and by now they both had many questions about electricity and so the next Saturday they took their questions to the local power station electricity is the movement of electrons now this was the first thing they learned from Mr Gibbons the engineer at the power station but now what is an electron a tiny negative particle Mr Gibbons explained an electron is so tiny that a piece of wire only one in long can hold more electrons than there are drops of water in all the o of the earth think of that now when David scuffed his feet across the rug he actually scraped electrons off the rug onto his shoes he became charged with electricity of course you can't see electrons not on your shoes nor even through a microscope they're the tiniest things we know about these electrons will jump off the first chance get as when David touched the radiator David figured that Marilyn's Cole must have scraped electrons from her hair and from her skirt but why did the comb pick up the Bits of Paper Mr Gibbons told them that these electrons or negative particles are always trying to get together with positive particles now we usually say it this way unlike particles attract each other so when the comb got to be negative it attracted the positive paper now David recalled hearing that like particles push each other away or repel each other Marilyn wanted to know what all this had to do with the wet cell that David made with the strips of copper and zinc so Mr Gibbons explained the chemical action of the soda water causes the copper to give off electrons these replace electrons which are attracted to the zinc then said David if there's a complete path the electrons flow through the wire and through the meter and back to the copper and if the circuit is broken the electrons pile up there they repel the other electrons behind and the flow stops yes David caught on quickly concerning the movement of electrons and why circuits must be complete for current to flow now Mr Gibbons asked whether they knew the difference between a conductor and an insulator Marilyn said that copper wire is a conductor it will carry electricity but glass will not how can we test what materials are conductors we use a battery a meter and two wires in a tester like this the needle swings if the material conducts electricity and stand still if it does not the plastic handle is an insulator David was thinking about making a tester at home when the magnet reminded him is the electricity in their home really made with magnets well a long time ago people found out that a magnet makes iron filings move into a pattern like this this shows that around the magnet there are lines of force and then about a hundred years ago a man named Faraday discovered that a wire passed across these lines of force generated a small amount of electricity in other words electricity can come from magnetism not long after another scientist discovered an effect when electricity has passed through a wire this produces the same sort of lines of force as a magnet does proving further connection that magnetism can be made with electricity a coil of many turns of wire makes many magnetic lines of force and a soft iron core in the loop makes the magnetism even stronger in fact the soft iron core becomes an electromagnet as long as the current flows if it stops for a moment the electromagnet drops the filings when the electromagnets lines of force are cut by a coil of wire a much stronger current is generated then Mr Gibbons brought out a small Magneto generator and it was fun to see electricity actually being generated David looked at the magnets and at the coil of wire which passes through the lines of force when turned now this is the principle of the generators that Supply the city with electricity in the PowerHouse the enclosed generators are turned by steam turbines in some parts of the country great dams hold back huge quantities of water and release it to turn water turbin which Drive the generators from generating stations current is sent out to factories offices stores and homes this electricity as we have seen is related to the static electricity the comb made in Maryland's Hair and to the current electricity made in David's copper zinc cell tremendous amounts of electricity for our everyday uses are made by passing wires through magnetic lines of force as in the PowerHouse where Mr Gibbons has been so helpful at home they both continued with their new adventure in electricity David started building a tester to find out more about many conductors and insulators Marilyn began making a scrapbook planning to put in pictures showing how we use electricity in our homes of course this was only a beginning because with electricity being used for more things every day there's always something new and fascinating to learn about it for instance you might find it interesting to learn how many different ways electricity has been used in making this motion picture [Music]