Elementary Charge Bozeman Science English English (auto-generated)

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hi it's mr. Andersen and this is ap

Hi. It's Mr. Andersen and this is AP Physics essentials video 8. It is on elementary charge,

physics essentials video 8 it's on elementary charge which is the smallest

which is the smallest unit of charge that an object can have. And it was determined

unit of charge that an object can have and it was determined by Robert Millikan

by Robert Millikan in the Millikan oil drop experiment. And what he was doing was dropping

in the Milken oil-drop experiment and what he was doing was dropping oil

oil through a little hole. And then using a microscope to see how he could change the

through a little a hole and then using a microscope to see how he could change

voltage to make the oil drops hover. And as he did that he found elementary charge. And

the voltage to make the oil drops hover and as he did that he found elementary

what he found is that that charge was either no charge or a multiple of a positive x or

charge and what he found is that that charge was either no charge or a multiple of a positive x or an

an elementary charge or a negative x. But it was never in the middle. In other words

elementary charge or a negative x but it was never in the middle in other words

charge is quantized. What that means is that charge smallest unit is going to be 1.6 times

charge is quantized what that means is that charge smallest unit is going to be

10 to the negative 19th Coulombs. Sometimes positive, sometimes negative, but never in

1.6 times 10 to the negative 19 coulombs sometimes positive sometimes negative

the middle. And so electric charge is quantized. What that means is it is indiscrete units.

but never in the middle and so electric charge is quantized what that means it's in discrete units and this was

And this was calculated to be 1.6 times 10 to the negative 19th Coulombs. We now refer

calculated to be 1.6 times 10 to the negative 19 coulombs we now refer to

to this as elementary charge. And so if you are looking at protons and electrons they

this as elementary charge and so if you're looking at protons and electrons

are both going to have charge. In electrons it is going to be a negative elementary charge.

they're both going to have charge and electrons it's going to be a negative

And a proton is going to be a positive elementary charge, even though protons have a much larger

elementary charge and a proton it's going to be a positive elementary charge even though protons have a much larger

mass, the charge is going to be the same. And so if we look at Millikan's experiment

mass the charge is going to be the same and so if we look at Millikan's

what he had set up was an atomizer up here. It is kind of like squirting perfume out.

experiment what he had set up was an atomizer up here it's kind of like squirting perfume out what was being

What was being squirted out were these little drops of oil. He then had a microscope down

squirted out were these little drops of oil he then had a microscope down here

here and then two charged plates. And so he could look at the oil as it falls right down

and then two charged plates and so he can look at the oil as it falls right

this hole right here. And he could change the voltage applied to those plates. And then

down this hole right here and he could change the voltage applied to those plates and then x-rays as well and we'll

x-rays as well. And we will get to those in a second. So let's look at one of these oils

get to those in a second so let's look

as it drops. And so what happens? Well it is being acted on by gravity. And so if we

at one of these oils as it drops and so what happens well it's being acted on by

look at that one drop of oil there is a gravitational pull that is pulling it down. But as it falls

gravity and so if we look at that one drop of oil and there's a gravitational pull that's pulling it down but as it

there is going to be air resistance as it moves through air. It is based on the viscosity

falls there's going to be air resistance as it moves through air it's based on

of the air. And so he was able to figure out that all of these drops should fall. So if

the viscosity of the air and so he was able to figure out that all of these drops should fall so if we take another

we take another drop right here it will just fall down to the bottom. But what he used

drop right here you'll just fall down to the bottom but what he used was an x-ray

was a x-ray tube. And what that x-ray tube would do is fire x-rays across that hole.

tube and what that x-ray tube would do is fire x-rays across that hole and what it

What it would do is it would knock electrons off or sometimes certain atoms would gain

would do is it would knock electrons off or sometimes certain atoms would gain

electrons. We know this now that it is built on the charge. But watch what happens if we

electrons we know this now that it's built on the on the charge but watch

take one of these and now drop it. What happens to it is it moves down but then it is in electromagnetic

what happens if we take one of these and now drop it what happens to it is it moves down but then it's in electro

field. And so since it is charged it is being attracted to this positive charge up here.

magnetic field and so since it's charged it's being attracted to this positive

And so what Millikan could do is he could regulate the amount of that voltage and the

charge up here and so what Millican could do is he could regulate the amount

oil would go up. And the oil would go down. And he could get it so it would balance out.

of that voltage and the oil would go up and the oil would go down and he could get it so it would balance out and then

And then he would just measure that voltage. And so once he did the physics of, okay we

he would just measure that voltage and so once he did the physics of okay we've

have a gravitational force down. We have got viscosity going up. But now we have got this

got a gravitational force down we've got viscosity going up but now we've got

electromagnetic charge. He was able to calculate, based on the size of that droplet how much

this electromagnetic charge he was able to calculate based on the size of that

is this elementary charge. And so he determined it to be 1.6 times 10 to the negative 19th

droplet how much is this elementary charge and so he determined it to be 1.6 times 10 to the negative 19 coulombs and

Coulombs. And so now we refer to that as the elementary charge. And he was like one percent

so now we refer to that as the elementary charge and he was like 1% off

off the value. So it is an incredible experiment. And so we can have charges of 0, no charge

the value so it's an incredible experiment and so we can have charges of zero no charge or we could have

or we could have elementary charges in the positive or elementary charges in the negative.

elementary charges in the positive or elementary charges in the negative in

In other words there is charge quantization. What that means is you can not have a charge

other words there's charge quantization what that means is you can have a charge

in the middle. You can not have like a half of a charge. Now if you are really smart and

in the middle you can have like a half of a charge now if you're really smart

you have watched all of the videos so far, that might not make sense. Because when we

and you've watched all the videos so far that might not make sense because when

were talking about a proton, a proton you know is made up quarks. And those quarks have

we were talking about a proton a proton you know is made up of quarks and those

partial charges. Remember each of the up quarks are going to have a two-thirds positive charge.

quarks have partial charges remember each of the up quarks are going to have a two-thirds positive charge and that

And that down quark is going to have a negative one-third e or negative one-third elementary

down quark is going to have a negative one-third or negative one-third

charge. But those quarks do not exist by themselves. They always are together as one object. And

elementary charge but those quarks don't exist by themselves they always are together as one object and you can see

you can see that they all add up, if I add up all of those charges, to 1 or a whole number

that they all add up if I add up all those charges to one or a whole number

of the elementary charge. And so again, if we are looking at an atom, what is it made

of the elementary charge and so again if we're looking at an atom what's it made

up of? Protons and neutrons and electrons. So those protons are in the nucleus with the

up of protons and neutrons and electrons so those protons are in the nucleus with

neutrons and then electrons outside. Protons have a positive e or a positive elementary

the neutrons and then electrons outside protons have a positive Y or a positive

charge. Neutrons have no charge. And electrons have a negative e. Even though the mass of

elementary charge neutrons have no charge electrons have a negative e to be

all of these objects is going to be different. And so did you learn to challenge the claim

different and so did you learn to

that an electric charge smaller than the elementary charge has been isolated? Again it is quantized.

challenge the claim that an electric charge smaller than the elementary charge has been isolated again it's

And I hope that was helpful.

quantized and I hope that was helpful

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