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can you calculate the electric field due to each charges separately?
Can I do it? No, I understand that's what I think I have to do, but I just don't know how :/
how do you calculate electric field due to a charge Q at origin at point (x,y)
yes ... use coloumd law to calculate electric field.
first try my problem (it's easy) ... draw picture, then we will try yours.
what is your problem?
a charge of magnitude Q is at origin, calculate electric field at (3,4)
Just to make sure is this the equation I have to use? \[F = k (|q_1q_2|)/r^2\]
yes ... E = F/q
how do I find r? that's one of the things that has been confusing me
would it be: \[F = ((9 x 10^9) (Q) )/ 5\]
that is 9 x 10^9
so, I'm guessing im wrong? :/
so would that be 25 instead of 5 then.
is Electric Field scalar or vector?
do you know that vector has components?
how do you find the two components of this vector?
draw figure ...
|dw:1378573584100:dw| do you know how to find Ex and Ey?
Ex = 3cos(angle) Ey = 4sin(angle)
I think :/
No .. must be Ex = E cos(angle) Ey = E sin(angle) find angle and put the value of E from above that you calculated.
Oh okay, but to find the value of E don't I still need a value for Q, you never told me what the charge is equal to, you just said it was Q
put put it Q for a while ... it doesn't matter ... express it interms of Q if you like you can put Q=1C
I got E = 3.6 x 10^8
seems okay http://www.wolframalpha.com/input/?i=9*10%5E9%2F25 find angle
But I'm still missing what Ex and Ey equal. Like I have two unknown parameters
like let's say Ex = Ecos(theta) I'm missing Ex and theta
angle ... calculate the angle
Theta = Cos^-1 (Ex / E ) ?
i got 90 degrees
use that ...
Ex = 1.98 x 10^8 Ey = 2.64 x 10^8
let me give you another problem.|dw:1378574722719:dw|
oh ok, just one thing i was still confused on earlier did you say that r^2 = (sqrt) x^2 + y^2 OR r = (sqrt)x^2 + y^2
\[r^2 = x^2 + y^2 \] pythagoras formula
it should be the second one
im working on them atm, im almost done
did you calculate Ex and Ey for this?
working on it right now
r^2 = 20 (theta) = 63.435 E = 9 x 10^8 Ex = 4.02 x 10^8 Ey = 8.05 x 10^8 I hope it's right >.<
all righ t... good. |dw:1378575628864:dw| Now i put both of them here.
Would I just add my answers from the two previous questions?
no ... not exactly. you add Ex1 + Ex2 and Ey1 + Ey2
oh ok. but technically wouldnt my Ex2 and Ey2 be the same, since it's the same charge in the same positin. I would just have to calculate Ex1 and Ey1 from the origin using a 2C charge instead of the 1C charge before
They are the components ... X components add up to X and Y to Y
finally find total Ex and total Ey
I got answers but idk it if it's right, but I did try my best
Ex = 8.702 x 10^8 Ey = 1.4525 x 10^9
sorry that took long
|dw:1378576951064:dw| where is your grand Ex and Ey,, use pythagoras theorem to calculate the grand E
oops, forgot that one
Etotal = 1.6947 x 10^9
also find the direction.
If I understood the question correctly, Theta = 59.10 degrees?
maybe ... i didn't calculate. but you know how to do your problem right?
i can try. but it'd be nice if I had someone confirm it afterwards
my problem is similar to the 3rd example you just showed me right
sure ... you show me what you did step my setp, i'll confirm.
Alright, i'll start with a sketch
Oh just to make sure. My charges are in nC, do I convert to C? also my locations are in meters, do I convert to cm?
is the sketch correct?
sorry ... i was lost. you should have pinged.
i didnt know how to ping. but how come q2 is 10^-9 but q1 is 10^9
@sean1372 nC = nano Coloumb do you know how huge 1C charge is ?
wait what? im confused now
1nC = 1x10^-C Coulomb. 1 coloumb is a huge amount of charge.
ooh since q1 is a -4.00 nC the negatives cancel out so that's what makes it a -4 x 10^9 and since the other charge is +6 it becomes a 6 x 10^-9
so the charges are -4.00 x 10^-9 C and 6 x 10^-9 C?
ive spent nearly 3 hours on this problem now.....
are you saying yes to the charges?
yes -4nC = -4/1000000000 6nC = 6/1000000000
okay can you check this so far. E1 = (kq1) / r^2 = (9 x 10^9 )(-4 x 10^-9) / 1 = -36 E2 = (kq2) / r^2 = (9 x 10^-9) (6 x 10^-9) / 0.36 = 150
seems okay ... calculate the components.
awesome, alright let me get on it :)
also careful about sign
on which one?
one is minus and another is +
instead of adding you will be subtracting.
oh yea. gotcha
I got: Ex1 = -21.60 Ey1 = -28.6 Ex2 = 150 Ey2 = 0 Ex = Ex1 + Ex2 = (-21.60) + 150 = 128.4 Ey = Ey1 + Ey2 = -28.8 + 0 = -28.8 E = (sqrt) Ex^2 + Ey^2 = (sqrt) (128.4)^2 + (-28.8)^2 = 131.59 N/C Direction: (phi) = cos^-1 (128.4 / 131.59) = 12.64 degrees
all right ... seems okay
yey I just put in my answer for part A (132 N/C) and it was right
part B was wrong though this is what it says: Calculate the direction of the net electric field at the origin due to these two point charges (Phi) = ______________ ∘ counterclockwise from +x-axis
(phi) = cos^-1 (-28.8/128.4)
it said that was wrong to
that can't be wrong ...just make wrt x axis.
does the "Counterclockwise from the +x direction" have to do with anything
if i were you i would do 2pi - tan^(-1)(..____)
how much degree will you rotate?
wait a minute... you told me to put cos^-1 (-28.8 / 128.4) I think you meant to put tan^-1(-28.8 / 128.4)
sorry ... i didn't see that ... i copied your text and edited.
it's fine. I got -12.64 instead now
if you want to find angle, cosine is a bad choice. cosine is +ve on first and 4the quadrant.
yea, but i dont think the answer would be -12.64 either. because i already tried +12.64 and usually if the answer is correct, but you have the wrong sign, it just tells me to check my signs. but it just told me that it was wrong
I mean I can still try it, but i hate to keep loosing point on it
i don't know what to do with that pic right now
Ex = Ex1 + Ex2 = (-21.60) + 150 = 128.4 Ey = Ey1 + Ey2 = -28.8 + 0 = -28.8|dw:1378582017447:dw|
you want answer is degree or radians?
90 + 12.64 http://www.wolframalpha.com/input/?i=arctan%2828.8%2F128.4%29
no, it didn't work either.
Calculate the direction of the net electric field at the origin due to these two point charges. ϕ = ∘ counterclockwise from +x-axis
i don't know what we're doing wrong. I didn't think the angle part would be more difficult then the electric field calculation
what do I do with that
oh dang, it worked! what did you do?
oooh you did 180 - 12.64
|dw:1378582825574:dw| + means go away - means come towards rest is just diagram, vectors, coulomb and Pythagoras.
I can't thank you enough. I know we spent a lot of time on this but I actually learned how to do this sort of problem. I know I was a bit slow at the start, I had just woken up and wasn't fully focused yet. But again. thanks for the help man
well I guess I'll see you around :)
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