Measurement Of Electricity

[Music] we use electricity in so many ways that we take the supply for granted but sometimes we have to measure it as Don found one evening he needed better light at his table to work at his hobby of flashlights and electrical cells but as he went to plug in his work lamp hold on I better not plug in here it looks as if mom is getting ready to iron some clothes and with that heater going to dry the baby's things why that's just the way we blew a fuse last week don't want to do that again have to figure out what we can do before Mom comes to iron let's see this takes 750 wat at 120 volts and the fuse let me see it's like this one 15 ampers have to figure this out wish I knew more about these things bolts Watts hampers what are these things what is a vol I'm Bolter I'm Bolter see here I am over here in your book alesandro Bolta perhaps I can help you to think what is this bolt that they call after me after you yes I produce the first source of bolts or voltage with a copper zinc cell oh we've made them in school yes I know simply copper and zinc in a solution of water and soda and you have a cell like the one I made over a century ago with that I discovered that electricity flows as the result of electrical pressure or voltage as you now call it electrical pressure I don't quite understand what do you mean volt is a unit of the force that moves electrons As you move say your lawn mower you must make the pressure with your hands to make it move the more push or pressure the better it goes now in electricity you use a voltmeter as a pressure gauge to measure the push or pressure of the electrons in volts now your fresh copper zinc cell how much pressure oh about one volt you know I'm catching on Volts measure electrical pressure huh I'm a poet volts measure electrical pressure pressure the pressure in volts is one factor that determines how much current goes through a circuit what's that again current how do you measure current oh that is where I come in I am aair I over on the next page Andre aair I discovered how electrical current flows so the unit of movement of electricity was named after after me okay so it's named after you what is an Amper well ampere as you call it now is a measure of current flow how can I explain uh have you some pennies in your pocket so imagine that each penny represents a billion billion electrons now if you move six pennies or 6 billion billion electrons past a point each second you have a current of 1 ampere wow electrons are so tiny that billion electrons per second is not a practical unit of measure so you use ampere as a measure of current flow just as in a gas pump the flow of gasoline is measured in gallons per minute I get it ampers measure flow of current current that's forced Through The Circuit by pressure measured in volts but depending on resistance that's where I come in I'm oh George oh I discovered that various materials have different electrical resistances let's see resistance that's sort of what holds back the lawnmower isn't it yes my name m is a unit of resistance how hard it is for the electrons to move could I see how that works with my dry cells here certainly take that bulb the one from the two cell flashlight and wire it to the cell now that dry cell can push with a certain pressure yes 1 and 1/2 volts and when you complete the circuit the dry cell pushes a certain amount of current through through the bulb yes current that's measured in ampers but it's not very bright well the bulb has a high resistance let us try the pressure from two batteries hook them positive to negative the way they are in your flashlight then the voltages are added you see to get past more resistance in the same way requires more pressure let's see two cells of 1 and 1/2 volts each should add up to 3 volts of pressure that's what it measures all right 3 volts now does that pressure make it brighter it should push more current through the more volts you have the more ampers you push through but if there are more ohms of resistance less ampir get through my law ohms law is important to you the current in ampers is equal to the pressure in volts divided by the resistance in ohms or simply ampers equals volts over ohms that's neat now I can figure all sorts of current flows so that flashlight bulb has a resistance of about 6 ohms with two cells just now how much current flowed through it let's see the current in ampir we said two cells have 3 volts of pressure but there's resistance 6 ohms why the current is 5/10 of an ampere you can also figure current where you know only the volts and the Watts what what is a what perhaps I can help you L my name is what James Watt my steam engines were the source of power for the early electrical generators the watt was named after me it is a unit of electrical power what a unit of power I it is just like horsepower you've heard of a 4,000 horsepower locomotive horsepower that's a unit of rate of work done so much work done in so much time work per hour that's horsepower see I'm AET too but remember the time element Watts also are a unit of power work per hour like horsepower your pennies that represent electrons pushing so many electrons per second past a point with so much pressure takes power in Watts so electrical power is the product of multiplying current times the pressure behind it 1 watt is equal to 1 Amper multiplied by 1 Vol so this 100 wat bulb under pressure of 120 volts carries uh a little less than one Amper that's correct now about your problem mother's iron over on the counter has a power of 1,000 Watts has it not and is made to operate at 100 20 volts so the current is over 8 ampers I catch on to find the ampers divide the Watts by the volts and that heater takes 750 watts that's more than six ampers now that plus over eight from the iron makes more than 14 and if I had one from this bulb no wonder the fuse blew oh golly that must be me sleeping at the table oh those men those units of measuring electricity volt Amper oh watt power ohms law I must have dreamt it all now Don can figure just how much power can come through that 15 ampere fuse can [Music] you