Electromagnets (1961)

[Music] [Music] one fine spring day after school Larry Smith was riding down the alley on his bicycle it was wonderful weather to be out and uhoh that in that Barrel seems funny to throw away such a new looking doorbell sure we'll be fine to play with though K Larry's little sister thinks Larry is a wonderful brother and she is always interested in everything he he does take that doorbell for instance Kay wants to know what Larry is going to do with it Larry is going to take the doorbell down into dad's basement workshop and see if he can make it operate Larry has been studying science in school and he believes he knows how to make this doorbell work several minutes later Larry is hard at work trying to make the bell ring though the Bell is connected to a dry cell it won't ring it's just more than Larry can figure out so K is sent for help Big Brother Bill can usually be counted on to help with such problems now let's see what the trouble is here well the electromagnet has a broken wire and isn't operating electromagnet what's an electromagnet asks Larry well we had better start from the beginning answers bill you two get some wire and nails and I'll get some other things now this is an ordinary permanent magnet what do you remember about magnets yes k a magnet attracts things of iron or steel it attracts the needle of a compass too now do you suppose this copper wire is is a magnet well it won't pick up these small nails but maybe it just isn't strong enough let's try it on the compass if it is a magnet it will make the needle move it doesn't so it isn't a magnet now let's see what happens when the wire carries an electric current we can start the current flowing by attaching the wire to an El electric dry cell now the compass needle moves the electricity has given the wire magnetic force but it still hasn't enough Force to pick up the nails can we make it stronger when we connected the wire to the dry cell the electric current flowing through the wire caused the wire to have magnetic force enough force to move the compass needle but since the magnetic force is spread along the whole length of the wire no part of it is strong enough to pick up the nails now Larry wind the wire into a tight coil around this pencil and see what happens the magnet is stronger but not yet strong enough to pick up the nails now let's give our magnet an iron core we can do this by putting an iron nail inside the coil instead of the pencil now try it K it works let's see why it works works the weak magnetic force which was spread out along the straight wire becomes stronger as the wire is coiled because this concentrates the force into a smaller space the iron nail makes an easier path for the magnetic force to concentrate inside the coil and makes the magnet stronger now K let's try our magnet on something heavier like this wrench no it isn't strong enough how can we make it stronger that's right Larry we made it this strong by coiling wire around the nail why not try even more wire good stronger now but still not strong enough how can we make it still stronger K do you have any ideas that's good K we can get more electric current with two dry cells instead of one and this should make our magnet stronger yes this time it works more electric current has done the trick a magnet that uses electricity to do its work such as the one we have made is called an electromagnet ours is strong enough to lift only small pieces of metal but in junkyards and steel mills big electromagnets are used to move heavy loads these electromagnets are so strong because they have miles of wire in them and they use a great deal of electric current and do you notice how this big electromagnet not only picks up its load but also drops it in exactly the right place that's something a permanent magnet can't do do you suppose we can make our magnet drop the piece of iron when we want it to of course we can by simply opening the electrical circuit we can control our magnets simply by opening and closing the electrical circuit that's what makes the electromagnets so useful not only for lifting things but for a great many other purposes for instance can you guess what this is like the electromagnet pulls the metal strip down and makes it strike the Bell actually almost the same thing happens in a real electric Bell only much faster than we can do it by hand but to make the electromagnet and our Bell work we must have a closed circuit if the wire is cut or broken we have an open circuit and the bell won't ring that's the reason your doorbell won't work it has a broken wire we can close the circuit by simply twisting the broken wires together now your doorbell is almost as good as new now that we have repaired the doorbell well let's review some of our facts about electromagnets a Wire by itself has no magnetic force but it does have magnetic force when there is an electric current flowing through it we can concentrate this Force by winding the wire into a coil and make it stronger by giving the magnet an iron core we can make it still Stronger by using more wire or by providing more electric current electromagnets work only when there is electricity flowing through them we control them by turning the electricity on and off doorbells have electromagnets in them and so do many of the other everyday things around us the bell in your telephone rings by means of an electromagnet and if we could look inside this electric motor we would see electromagnets there too yes the electromagnet is one of the many wonders of electricity one of the many ways in which we make electricity work for us and what interesting things our friends have learned from the electromagnet in the broken doorbell and from their big brother [Music] Bill