Question

Here's the question.

https://s18.postimg.org/bvwkg2zax/Screenshot_20171031-214236.png

Answer 1

wait let me upload the actual question.

Answer 2

@563blackghost

Answer 3

Find the total electric potential at the midpoint of the side between charges 2 and 3.

Answer 4

@shadow

Answer 5

Where is 2 and 3?

Answer 6

Oh in the link. Blocked w/school wifi, got it on my phone

Answer 7

\[PE = K \frac{ q _{1} \times q _{2} }{ r }\]

Answer 8

\[K = 8.99×10^9 N m^2 C^−2.\]

Answer 9

shadow. sorry bro. i was werking on the question which i just finished. btw tell me if this question is similar to what i've posted up there.

Answer 10

for your first problem, they want potential (V), not potential energy (U).

potential (V) has units of Joules / Coulomb, aka Volts.

you can measure potential at the midpoint of 2 and 3 by placing a hypothetical *unit* (ie 1C) test charge there.

and, if you actually did that and released it, the test charge would fly off in the direction of \(F_{\text{net}}\) as per the drawing. the force on the unit charge due to the charges at 2 and 3 cancel out, as drawn.


at that singular point in time, the potential would be \(V = k\dfrac{q_1}{d}\)

the second problem is the same idea with slightly different geometry. again, exploit the symmetry.

you are only being asked about that point in time in which the symmetry applies.

a lot of EM is about setting stuff up the right way to keep the analysis simple.

my first + last word on this thread :)

Answer 11

Hi Billy.

Can you please check my diagram? Thanks!

Answer 12

look at the symmetry

forget about what you have done thusfar.

Answer 13

good luck !!

Answer 14

I suggest you find the distance between the midpoint and each charges first (2:3 ratio if I'm not mistaken), once you've got "r" then you can use V=kq/r for each charge then find the total V by adding them up

Answer 15

ok so again. do i need to find the distance from charge 1 to the mid-point?

Answer 16

thats what i was about to say.

Answer 17

sam can u plz work with me?

Answer 18

Yeah, I'm pretty sure there is an easier way though

Answer 19

i'll draw to make this fast.

Answer 20

is my midpoint right?

Answer 21

wait wait wait. you have the wrong diagram sam :/

Answer 22

Really? Show me your current problem

Answer 23

that was just an example from my course work. :/ sorry i didnt know what i was doing to i pulled out an example problem

Answer 24

https://s18.postimg.org/bvwkg2zax/Screenshot_20171031-214236.png

Answer 25

No problem

Answer 26

and this is the question.

Answer 27

this is what i drew based on the description.

Answer 28

wow!! :O

Answer 29

btw is the distance from the midpoint to charge 1 =

Answer 30

if my distance is right can i use the following equation to solve for the electric potential?!?!? by using this formula.

Answer 31

I forgot how electric potential works but I think its similar to electric force, just the formula's different,
First \(V_A\) on point X,
\[V_A= k\frac{q}{r}= 9\times10^9 ( \frac{4\times10^{-5}}{\frac{\sqrt{5}}{20}})\]
Then \(V_B\) and \(V_C\) on point X,
\[V_B= k\frac{q}{r}= 9\times10^9 ( \frac{4\times10^{-5}}{0.05})\]
\[V_C= k\frac{q}{r}= 9\times10^9 ( \frac{4\times10^{-5}}{0.05})\]
Then \(V_A\)+\(V_B\)+\(V_C\)
This is probably how it's done, I'm not sure myself though, do we have a potential between two equipotential charges?

Answer 32

nope no volts are given in the question.

Answer 33

We're trying to find the electric potential at the midpoint between charge B and C, not the midpoint of the triangle

Answer 34

Well electric potential is V isn't it xD

Answer 35

yup electric potential is volts.

Answer 36

I need to refresh on this, I haven't done E&M for quite a while

Answer 37

:/

Answer 38

So from this
https://courses.lumenlearning.com/physics/chapter/19-4-equipotential-lines/
Like charges repel, so the only E potential will be coming from \(V_A\) only

Answer 39

wait 1 sec.

Answer 40

im looking

Answer 41

\(V=4.1569 \times 10^6V?\)

Answer 42

yeah its the same thing but since we are asked to find the total eletric potential of charges 2 and 3....i think we need to modify the equation a little like this..

Answer 43

wait let me show you a question example from my course...pretty much the same question i think.... wait.

Answer 44

here!!

Answer 45

i think this is it!

Answer 46

Wait, yeah we're solving it actually hah

Answer 47

but there's a slight difference. We're only dealing with Q2 and Q3

Answer 48

wait i need to go blow my nose. 1 sec

Answer 49

Why, Q1 still has an effect on the midpoint between Q2 and Q3

Answer 50

really?

Answer 51

The distance from charge Q1 to the midpoint between charge Q2 and Q3
\[r=\sqrt{0.1^2-0.05^2}=\frac{\sqrt5}{20}m\]

Answer 52

damn!! :O

Answer 53

wait how???? give me a few seconds to take it in.

Answer 54

This could be the final answer, 99% sure of it
I've freshened myself from a video before answering this
https://www.khanacademy.org/science/physics/electric-charge-electric-force-and-voltage/electric-potential-voltage/v/electric-potential-charge-configuration

Answer 55

refreshed*

Answer 56

oh you just added them all together at the end?

Answer 57

Wait you're right hahah I made a mistake there

Answer 58

Yeah

Answer 59

sam i dont think we are dealing with Q1 pal.

Answer 60

Correction
\[V_A= k\frac{q}{r}= 9\times10^9 ( \frac{4\times10^{-5}}{\frac{\sqrt{3}}{20}})=1.039 \times 10^6V\]
\[V_A+V_B+V_C=15.44\times 10^6V\]

Answer 61

Why do you think we're not dealing with Q1?

Answer 62

cuz look at the example i gave you dealing with midpoint problem.

Answer 63

are you sure fam?

Answer 64

Yeah? Charge Q2 and Q3

Answer 65

actually you are right that Q1 has to have some type of effect of charge 2 and 3

Answer 66

Q1 is in the vicinity so it has to have an effect on the problem and it isn't far too

Answer 67

yeah cuz if we look at the distance ...its not actually that far,.

Answer 68

Similar with the example problem you gave me, the question asked "Find the total electric potential at the midpoint of the side of the triangle, between charges 2 and 3".
It didn't say anything about charge Q1 but we still got to deal with it cos it has an effect on any point

Answer 69

yes sir. bows*

Answer 70

You're welcome, feel free to ask if you have any doubt

Answer 71

AWW Tears*

Thanks you so much for your time and effort......like i can't even....Hugs*

Answer 72

No problem xD, glad I'm helpful

Answer 73

:)