What Is Electric Current? (1961)

[Music] [Applause] [Music] la wa must you blow that horn I can't help it it's stop let's fix in a car the source of electric current is the battery after the horn has been fixed and the battery is properly connected again it permits us to have light heat and power the starter motor is run by electric current from the battery we can also use house current to get light heat and power but house current is too dangerous to experiment with instead we'll use the battery we have connected some of the same things to the battery that are connected to it in the car headlights a horn and a starter motor we've also included this meter the meter indicates whether or not there is electric current in the circuit when the needle in this meter points straight up the meter reading is zero there is no current in this circuit now why isn't there the answer of course is here there is electric current only when the electricity has a complete circuit to flow through now the electricity has a complete circuit to flow through when the circuit is broken no electricity flows through it when there is an electric current the meter shows it by completing the proper circuit we can cause electricity to flow through the headlights or the horns or the starter motor but can we really see anything flowing through this circuit here is something that we can see flowing and here is a meter that indicates when water is flowing through a pipe the meter reads zero when the flow of water is stopped what happens if we turn on another sprinkler [Applause] too now there is more water flowing through the pipe and the meter reading is higher if we turn on another sprinkler the reading is higher still when you turn something on in this CC the meter shows a reading turn something else on to and the meter shows a higher reading this meter acts like the meter measuring the increasing flow of [Applause] water this is one piece of evidence to suggest that there is something flowing through these wires that acts in one way at least like water flowing through pipes if something is flowing in this circuit it must go out here and come back here or the other way around let's say for the sake of argument that it flows out through here along the wire through the meter making it give a reading through the closed switch through the headlights making them light and back along the wire to the the battery in other words for the sake of argument we're saying that electricity flows out from this post of the battery and flows back in to this post if what we've said is true now the electricity is Flowing out from here through this wire through the headlights through the switch through the meter making it show a reading and back to the bat yes the meter shows a reading but in the opposite direction reversing the wires doesn't seem to make any difference to the headlights they light with the wires in either position but look what it does to the meter the meter shows a reading when the wires are attached either way but the reading is in One Direction when they're like this and in the other direction when they're like this there is a similarity between the way the water wheel acts and the way this meter acts which suggests that both are being acted upon by something that flows in the one case water in the other case electricity between this battery and these headlights there are several thousand ft of wire when the switch is closed the circuit will be complete let's assume that when the circuit is completed electricity will flow from the battery out through this wire through the headlights and back through this wire to the battery If This Were true we might suppose that this meter would kick over before this one after all the electricity would have to go through all the wire before it gets to this meter let's try it and see no as far as the eye can see both meters kicked over at the same time what does that mean here is a loop of clear garden hose these meters will kick over when water flows through them when this pump is turned on it will pump colored water from this container out through the circuit of hose these two meters didn't kick over at the same time the water flowed through this one first and then through this one now the hose is full of water when we turn the pump on now water will will move everywhere in the circuit at just about the same time and the meters kick over at the same time why do these meters kick over together we could explain it in the same way by assuming that whatever it is that's flowing in this circuit is already in the wires the battery would be acting in somewhat the same way as a pump the wires like pipes that are already full of something that in flow the stuff in the wires that can flow is called electric charge when something pushes electric charges and makes them flow then there is an electric current we'll look at another piece of evidence that goes to prove that the electric charges are already in the wire this meter will kick over when electric charges flow into it when electric charges reach the piece of gold foil in this gadget the foil will move away from its support that doesn't prove the electric charges were in The Wire they could have come from the battery this is a plastic coat hanger and this is a silk scarf you've probably observed that rubbing things can sometimes cause electrical effects somehow the rubbed coat hanger is making electric charges move but the coat hanger doesn't touch the wire the electric charges must already be in the wire the coat hanger pushes electric charges into the meter and onto the foil Leaf When The Hanger is removed the electric charges flow back when something pushes charges and makes them flow you have an electric current don't think that electric charges are found only in such things as wires We Believe today that electric charges are in all materials we believe that any material in the universe has electric charges in it and there's lots of evidence to back that up don't try this yourself unless you use a weak battery there is electric current in this circuit electric charges in human bodies are being pushed by the battery and made to flow causing an electric current