Name: 02-4（Net electric field from multiple charges in 1D | Physics | Khan Academy）
Uploaded: 2022-07-19T03:06:50.000Z
Duration: 7 min 27 s
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- [Instructor] So it turns out solving electric field

形容詞比較級

let's say we wanted to know what's the magnitude

created halfway between these two charges down here.

So you've got a positive eight nanocoulomb charge

But what we want to know is what's the total electric field

So each charge is going to create an electric field

at this point, and if you add up like vectors,

those electric fields, what total electric field

Now at first you might think, well you should

It's very tempting to say that the electric field

because you've got a positive eight nanocoulomb charge

And to see why, first you should just draw

what is the direction of each field at that point?

So this positive eight nanocoulomb charge is gonna

create a field at this point that goes radially away

from the positive charge, and so it's gonna go to the right.

And I'm not even looking, so when I'm trying to find

the electric field from this positive charge over here,

I'm not even paying attention to this negative charge,

whether this negative charge is over here or not.

And now I can do the same thing, I can ask

what field would this negative charge create?

And I'm gonna pretend like this positive charge

So negative charges create a field that go radially in.

So over here radially in would point to the right.

The negative charge created a field radially in,

that was to the right, the positive charge created a field

these are gonna add up to twice the fields

you just add them up if they're in the same direction,

and you'll get two times the contribution

So it's not always the case, in other words

it's not always the case that a negative charge

Those electric fields might point the same direction,

So how do we find this net electric field then,

Well we're gonna say that, all right, this electric field,

the first thing I can say is this net electric field

So this is just really in the x direction,

all I really care about is the electric field

in this horizontal direction, and it's gonna be equal

So we'll do the blue charge first, that's gonna be k

times the blue charge divided by r squared.

Then we'll do the yellow charge, it's gonna be

plus k, the charge of that yellow charge,

So we'll plug in some values here, this k is always

and the q of this blue charge was positive eight

nanocoulombs, nano is 10 to the negative ninth,

I like using nano because then that negative nine

Think about it, I want the net electric field

so the r that I care about in this electric field formula

is the distance from the charge to the point

where I want to determine the electric field,

So for this case, from the charge to the point

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02-4（Net electric field from multiple charges in 1D | Physics | Khan Academy）

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assume

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