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Anonymous
2:27 AM
 
Anonymous
Why won't the field be zero?
 
3:25 AM
@ice I think we have a formula for this, Fields due to both parts add up
 
Anonymous
@samjoe Yes, I know they add up when the magnetic field provided by the wires is in same direction. Isn't it here in the opposite directions?
 
yeah you are correct!
 
Anonymous
There is no option as zero
 
Anonymous
I think there's a an error in the arrow of one wire.
 
That is possible, you can check by considering that case
 
4:12 AM
@IceInkberry i am not getting 0
 
Anonymous
@Jasmine How?
 
Did i do something wrong?
@IceInkberry @samjoe
 
Anonymous
@Jasmine I think you drew the digram as if P was above the point where the wires join and not in the plane, below it.
 
@IceInkberry oh so is it in the plane
Oh i see d
 
Anonymous
@Jasmine Atleast what it seems in the diagram.
 
Anonymous
4:20 AM
Because the answer is also not that way.
 
Whats the answer
 
Anonymous
44 mins ago, by Ice Inkberry
I think there's a an error in the arrow of one wire.
 
Anonymous
Solve this way, the answer is that.
 
@IceInkberry oh! And in plain wire current cant be in 2 direction also
If its not hypothetical
To remain in contact two surface must have component of velocity along common normal right?
 
4:40 AM
@JohnRennie morning are you free for sometime?
 
5:05 AM
@Jasmine I'm pretty busy with work this morning. Sorry :-(
 
@JohnRennie oh thats ok when you free please ping me!
 
 
2 hours later…
7:11 AM
@JohnRennie Are you there?
 
@Abcd is it quick? I have a meeting in 15 minutes.
 
@JohnRennie ya its quick
 
We've done something like this before haven't we? The trick is expand each plate into the sides of two capacitors. I can draw a diagram if that's not clear.
 
@JohnRennie pleas share the diagram
 
Diagram incoming ...
@Abcd Each plate behaves as if its two sides are part of a capacitor with spacing $d$. In the lower diagram I've shown this by expanding each plate into an H shape. I've coloured the plates to try and make it clear how the top diagram expands into the lower one.
 
7:28 AM
@JohnRennie thanks I can do it now.
I had forgotten this concept
 
Cool :-) Any moment now my phone is going to ring for the start of a meeting, so I won't be around for a while.
 
7:43 AM
@JohnRennie Good morning to you and everybody
@JohnRennie Can you ask an help, please?
 
@Sebastiano He is busy in a meeting right now
 
@Abcd Thank you very much. Can you ask my "excuse me" to him?
 
8:36 AM
@JohnRennie Are you free for 1 hr?
 
 
3 hours later…
12:04 PM
@JohnRennie whenever you get back,can you ping me
 
 
3 hours later…
2:54 PM
@harambe hi, I'm around now for a couple of hours
 
3:25 PM
@JohnRennie okay
I will ping you when I am done with some of my work
 
4:23 PM
Can you see explain the comment of user Farcher .....I am having a slight differenculty understanding it
 
@harambe that's not a link to a question ...
 
6
Q: Free body diagram of block on accelerating wedge

Kaumudi HConsider the following system: I am thoroughly confused about certain aspects of the situation described in this diagram in which a block is placed on a wedge inclined at an angle θ. (Assume no friction everywhere) Let us consider a few different cases: Firstly, when the wedge is accelerati...

Sorry for the mistake
 
You mean Farcher's answer?
 
Not the answer but the comment
 
@harambe The vertical acceleration of the block $z$ is the same for an observer standing by the wedge because the wedge does not move in the vertical direction. That observer would see the wedge accelerate at $X$ to the right and the block accelerate a little faster at $x$ to the right. Remember the block is accelerating down the incline. So acceleration of the block relative to the wedge is $x-X$ to the right. — Farcher 1 hour ago
That?
 
4:32 PM
Yes
Isn't the block having different vertical acceleration in ground frame and the observer is only having horizontal acceleration
Since the wedge is constrained to move horizontally and the observer is part of it
 
The block has some acceleration that we can express as horizontal and vertical components $(a_h, a_v)$.
 
Yea
 
The wedge frame and lab frame observers have different horizontal accelerations, so in their frames the horizontal component of the block's acceleration will be different.
But, both the wedge and lab observers have zero vertical acceleration. So in both the wedge and block frames the vertical component of the block's acceleration $a_v$ must be the same.
I think that's what Farcher means.
 
What is a lab frame BTW....I searched it up and it said it's the frame where the experiment is performed so isn't the wedge lab frame
 
Lab frame is what you've called the ground frame.
(at least I think that's what you meant)
It's the frame in which the floor is stationary.
 
4:39 PM
Okay
 
I have to go now I'm afraid.
I have a big programming job to do this week, so my time in the chat is going to be rather limited. Hopefully I'll have more time next week.
 
Okay ...good evening sir
 
 
1 hour later…
5:50 PM
file:///C:/Users/Swapnil/Downloads/s-block-elements.pdf
Is it fine if I study s block from here (only)? {for iitjee purposes}
 
 
1 hour later…
7:11 PM
@Abcd ?
 
@sammygerbil Hi, uploading in a minute.
@sammygerbil Please explain what exactly happens here?
 
@Abcd What are you not sure about?
 
@sammygerbil Why should work done by electric field forces be equal to work done by external agent and how to calculate it?
 
@Abcd As with the problem in Physics Q&A, you can use the Conservation of Energy to find heat produced or work done by external agent. The Stack Exchange answer will help you.
 
@sammygerbil just had a question based on the fundamentals
 
7:22 PM
:45695869 Yes?
 
Basically we would use 2W + kC(V^2-1)= 0
Which implies $W= \dfrac{-1}{2}(CV^2)(k-1)$
But we know that work of external agent is negative
and that of electric field is positive
1 min ago, by Abcd
Basically we would use 2W + kC(V^2-1)= 0
I mean why are we using this one^? Work of electric field and that of external force should cancel
so basically $Q= 1/2 CV^2 (k-1)$ (and not work)
Then how do we find the work?
Work done by all forces = $\Delta KE$= 0 (here)
 
:45696067 Are you reading from a worked solution? I am having difficulty following you.
 
@sammygerbil Okay, leave my solution... Could you please tell me what is to be done in the above question? I am not able to infer much from that SE answer
 
@Abcd Did you understand my answer on Physics Q&A site?
 
@sammygerbil yes I did
 
7:36 PM
@Abcd Do you think you can apply it to this problem?
 
@sammygerbil Like this: ?
Work done by all forces = $\Delta KE$
Work done by external force+ Work done by electric force = 0
Work done by resistive forces causing heat + Work done by battery = Delta KE
So heat produced = work done by battery force
but thats the wrong answer @sammygerbil
 
:45696372 Part (ii) here is the same kind of question : dielectric slab inserted while battery connected. Could you post your question and your answer on the Physics Q&A site? I have difficulty working on this in chat.
 
@sammygerbil Okay posting in a minute
 
@Abcd No, heat produced is not equal to work done by battery in the Physics Q&A problem. It is half the work done by battery.
 
@sammygerbil But I just proved to you that its equal to the work done by battery :(
What is wrong with my proof?
 
7:45 PM
@Abcd Work done by battery = increase in energy stored in capacitor + work done against external agent.
 
@sammygerbil but work done by external agent is cancelled by the work done by fringe electric field
 
@Abcd Where are you getting this from?
 
@sammygerbil there are only two vertical forces
the fringe electric field force and the external agent force
since accceleration is 0
both forces should be equal and opposite
Work done by all forces = Change in kinetic energy // Work Energy theorem

Work done by external agent + Work done by fringe electric field + Work done by battery force + Work done by resistive forces = Change in kinetic energy = 0

Now work done by external agent= -ve of work done by fringe electric field

Work done by battery force = EMF $\times\Delta Q = CV^2 (K-1)$

Work done by resistive forces goes in the form of heat

$\implies \text{heat produced} = CV^2(K-1) $
 
@Abcd Yes you are correct. The force applied by the external agent equals the force with which the capacitor is pulling the slab.
 
@sammygerbil then why am I getting the wrong answer
 
7:56 PM
@Abcd Please would you write up your answer in Physics Q&A. That would be easier for me.
 
@sammygerbil Yes, I have posted the question on Physics Q and A. Please reply there.
 
The battery is doing the work done by the fringe electric field. I don't know what the "resistive forces" are. Isn't that the force supplied by the external agent?
 
@sammygerbil resistive forces are the ones causing heat
 
The way I look at it is that the capacitor is "the system". The battery does work on "the system" equal to QV. The system does work on the external agent equal to QV/2, and is left with extra internal energy QV/2.
 
@sammygerbil Makes sense.
 
8:09 PM
The question does not ask for heat produced in step (ii). Maybe that is what is confusing you - it confuses me. It is not clear to me whether the same "resistive force" (ie resistance in the wires) is still present when the external agent does work in step (ii).
 
8:40 PM
Good evening. Is there any user that can you help me for my question?
1
Q: Multipole expansions: test on a function $\zeta=\zeta(t)$

SebastianoConsidering the potential $\psi(r)$ of a sphere with density $\rho(\mathbf r')$, connected by a small volume positioned in the $P'$ point as shown in the figure: The $\psi(r)$ is: $$\begin{align} \psi(r)=-G\iiint_{\mathcal{V}} \frac{\rho(\mathbf r')dx'dy'dz'}{|\mathbf r - \mathbf r'|}= -G\i...

Thank you very much.
 
8:51 PM
@sammygerbil Are you there?
 
@Abcd Yes
 
@sammygerbil I have a problem please see it:
@sammygerbil Would you like to know what I tried
 
@Abcd Er, no?! :) Are you not getting the right answer? I think there was a similar question in the chatroom yesterday.
 
@sammygerbil I am not getting the right answer :"(
 
@Abcd You can think of it as 2 capacitors in series.
 
8:56 PM
@sammygerbil I have checked yesterdays transcript there's no such question there
@sammygerbil Thats exactly what I am doing but not getting the right answer
 
@Abcd ok what is your calculation?
 
@sammygerbil let the two capacitors be in series with voltages V1 and V2
$V_1 + V_2 = 440 $
$Q_1= Q_2 \implies k_1C_1 = k_2C_2$
 
ok so far
 
$\implies V_2 = \dfrac{k_1C_1V_1}{k_2C_2}$
E in presence of dielectric $E_2 = \dfrac{E_{o2}}{k}= \dfrac{V_2}{d\times k}= \dfrac{440}{\left(1+\dfrac{k_1C_1}{k_2C_2}\right)k_1}$
$$\dfrac{C_1}{C_2}= \dfrac{d_2}{d_1}$$
@sammygerbil does it look correct to you
 
Thinking ...
$Q_1= Q_2 \implies k_1C_1 V_1= k_2C_2 V_2$
 
9:10 PM
@sammygerbil I just missed the Vs there while copying
But if you see down i have used the correct thing
coz I was copying from the solution in my notebook
 
Yes, you have.
 
@sammygerbil So whats the mistake in my solution?
 
Next line I think it should be E2=440/(1+k2C2/k1C1)d2k2
 
@sammygerbil copying error again its E_1
I have missed a d_1 there as well
$E_1 = \dfrac{V_1}{d_1 \times k_1} \implies E_1 = \dfrac{440}{\left(1+ \dfrac{k_1d_2}{k_2d_1}\right)\times d_1\times_k_1}$
$$E_1 = \dfrac{V_1}{d_1k_1}$$
Where $V_1 = \dfrac{440}{1+ \dfrac{k_1C_1}{k_2C_2}}= 350 V$
$$\implies E_1 = \dfrac{50\times 10^2}{3}$$
@sammygerbil Please tell me my mistake :(
 
9:29 PM
Sorry having difficulty following in chat. Maybe I'm getting confused, but I think E=V/kd is wrong. The electric field is E=V/d.
 
@sammygerbil electric field when dielectric is inserted is $E= \dfrac{E_o}{k}$ where $E_o = \dfrac{V}{d}$
@sammygerbil just out of curiosity whats the problem with chat?
 
What is E_0?
 
@sammygerbil Oh are you facing difficult enabling mathjax
Please see this to enable mathjax:
27
A: Any chance of MathJax in chat?

Ilmari KaronenAs a workaround while this request is pending, there exist several client-side workarounds that can be used to enable LaTeX rendering in chat, including: ChatJax, a set of bookmarklets by robjohn to enable dynamic MathJax support in chat. Commonly used in the Mathematics chat room. An altern...

Damn, if you faced difficulty because of mathjax, I am very sorry, I should have told you about this earlier.
Sorry I have to go in 7 minutes. If you get my error please ping me
 
Partly. But mostly because I prefer to have time to think about the problem.
ok
 
@sammygerbil Have you enabled mathjax now?
 
9:39 PM
No sorry I'm working on something else. But I will have a look at it soon.
 

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