Transcript of Julius Sumner Miller: Lesson 40 - Adventures in Magnetism

[Music] how do you do ladies and gentlemen and teachers and boys and girls I'm Julia Suna Miller and physics is my business and our very special business today I have entitled adventures in magnetism this is a marvelous subject because it is filled with enchantment and with many things we do not understand as you know there exist in nature some things which are naturally magnetic for example iron nickel Cobalt magnetic abundantly highly magnetizable but an added phrase everything is magnetic to more or less degree because magnetic phenomena have their primordial origin in the motion of electrons and since atoms of all kinds of stuff have electrons which are in motion everything is magnetic so everything can be magnetized to more or less degree some things very slightly of course just as everything can be electrostatically charged some to more some to less degree question how can I make a magnet here is something that will enchant your soul I have an iron bar iron is magnetizable it is magnetic stuff let me say that this has no magnetic history none I'm going to magnetize it I will put it in this place in this room in a north south magnetic Meridian which is determined by a compass needle here here is a compass needle which Points North and South somebody says well it doesn't Point North and South professor in this room no it doesn't because I've got lots of alien and foreign uh magnetic influence around but supposing this is the north south magnetic Meridian in this room which it is I'm going to take the iron bar hold it horizontally tip it a little now why do I dip it or tip it because here is a needle if we can get a look at this one there is a needle which shows a magnetic dip that's it not too reliable in its uh reading here and now because of the alien magnetic influences all around including the magnetic Personalities in this studio now what was I about to say when I was diverted here by this phrase yeah so the Earth's magnetic field has a horizontal component and a vertical component and that's why I'm going to do this to the rod and then with a hammer I'm going to strike it smartly as the British would say bang bang bang bang and I have made this by a magnet I have magnetized it proof let me approach one end of the bar to that needle watch watch uhuh it repelled the needle and repulsion is the only evidence that a sample of stuff is magnetized attraction proves nothing so I've made a bar magnet I made a magnet out of striking an iron bar how else supposing I take a bar of iron or other magnetizable stuff wrap a coil of wire around it and connect the B the the coil of wire to a difference of potential such as a storage battery I make an electromagnet here I'm going to do that I have a battery I have a wire I'm going to wrap this bar with the wire coil of wire I will show you that this is a feeble magnet from my earlier Adventure wh feeble notice no action no action now I'm going to energize the wire with an electric current and watch the effect on the end of that Rod watch it Aha and what else oh the wire's getting pretty hot sure so I have made a magnet by striking it I have made a magnet by energizing a coil of wire another here's a bar here's a hunk of stuff magnetite oh that raises a very good question magnetite is fe3 B4 and so I like to ask what is the veence of oxygen in this three ions for oh that's a good question but anyway going to make a magnet this stuff has astonishing properties uh load Stone it's called hang it up on a string and it will set itself in the Earth's north south magnetic line I'm going to make a magnet out of this bar which has no magnetic history watch me somebody says that that looks like something Mystic in fact regarding the hitting of that iron bar or this business that I'm doing here if I did that in my native New England in the 17th century they'd caught me off to a stake for madness but anyway I make this an iron bar by stroking or consider another better way here I have a bar that has been magnetized somebody says that isn't a bar Professor sure it is it's a bar whose ends have been turned up and it's a magnet Oho notice notice notice the motion this is the direction of the magnetic field that emanates from this Rod being magnetized so I can make a magnet in many different ways problem here is a bar of iron magnetizable stuff which I have scored a little bit with a file so that it's breakable now you know that if I have a horseshoe magnet a correction a bar magnet it has some definitive regions called poles South and North if I break that bar magnet as I have done here now with one already we discover that each one is a magnet so I have South north south north supposing I took a piece of stuff magnetizable which has no magnetic history and I make a magnet out of it let me do that watch it good now here's what we have we have a bar of stuff with some such polarity defined now I'm going to break it and what do I have a north south a South north I ask what is the pole strength of these separate pieces very good question another adventure in magnetism I have here two identical bars absolutely identical in every respect same thickness same length same stuff but I assert that one is a magnet and the other is not and I can't tell which one is question question without any accessories whatsoever no string to hang it up so it'll set itself in the earth's field no compass needle with which to test it no pins or nails to pick up how can you tell just by the interaction of these two which is the magnet and which is not let me show you the Dilemma a b they stick stick you get the idea they stick they stick going to turn that one around stick stick stick stick stick question just by handling these two how can I determine which is the magnet if I were a kindlier fellow I'd give you a hint but I won't wonderful little question next question iron is magnetic steel is magnetic nickel is magnetic Cobalt is magnetic question is stainless steel magnetic is stainless steel magnetic oh watch it piece of stainless steel horseshoe magnet very strong watch it well notice I don't think I'm going to show you because I think it's a very interesting question to leave unanswered is stainless steel magnetic well I'm a kind fellow so I'll show you watch it it is not now supposing I wanted to provide some magnetic shielding here is a sliver of Steel which is highly magnetic watch it sure highly notice the influence of the field at quite a distance I'm I'm going notice you can't live with immunity in the midst of this stuff I'm going to put a piece of zinc on there is zinc a magnetic insulator what no is copper a magnetic insulator no is aluminum a magnetic insulator no is wood a magnetic insulator no is lucide a magnetic insulator no here is a piece of iron iron is magnetic watch it sure let us see if this is a magnetic Shield watch it watch NOP not a magnetic Shield remember how thick it is watch it here is a thicker slab watch it oh that's magnetic all right is it an insulator watch because this is tricky watch it oh it looks like an insulator I'm going to do it again watch me cuz I'm sly and tricky watch it no it's not an insulator I am raising a very exciting dilemma here is a heavy slab of iron is it an insulator watch me now very cautiously watch me I'm going to show that it is an insulator yeah it's an insulator didn't pick that up now I'm going to do it again I'm going to show that it is not an insulator there it is I want you to worry about that and that's why I'm not saying anymore question supposing I had a bar magnet here and a bar magnet there and I sprinkled some iron filings between let's go down here and see that I have that very thing here here is a b magnet there is a b magnet I put a glass plate on top I'm going to sprinkle this with filings look at the beautiful array that results beautiful thing now supposing I had a bar magnet n there the S over here and S here the N over there I have a strong magnetic field there I want to insulate that region how could I do it beautiful if I sprinkled ion filings there they would take such a direction if now I put a heavy iron washer in there we would find an interesting thing that the field inside there would be field free the region there feel free meaning that soft iron is a very good magnetic insulator which is an exciting thing to recognize now some magnets ceramic discs watch it one one watch they are polarized facially and obviously light poles are adjacent and you see that I have them running on an aluminum rod it could not be magnetic are you not agreed that these magnetic phenomena are enchanting to witness and I thank you for watching [Music]