KVPY 2016 interview

@Spandan Senapati – Any idea about what he told your father? – Swapnil Das · 6 months, 3 weeks ago

@Spandan Senapati – Your interview went quite well plus aptitude marks = top 10 for you.

Congrats! – Harsh Shrivastava · 7 months ago

@Prakhar Bindal – Happy holi to all 😀 – Harsh Shrivastava · 6 months, 1 week ago

@Prakhar Bindal – Same 2 u bro ..... – Sanyam Goel · 6 months, 1 week ago

@Prakhar Bindal – Yup same to you.......... – Spandan Senapati · 6 months, 1 week ago

@Spandan Senapati – Thnx! – Harsh Shrivastava · 7 months, 4 weeks ago

@Aniswar S K – I have a nice question in physics. Will post it soon.Do try. – Spandan Senapati · 3 months, 3 weeks ago

@Aniswar S K – And to the other question(on pressure) that you had posted I got \(V^2=\alpha b/(k^2-1)\).If the dielectric slab completely fills the space then studying the distribution of charges the net field at position ofa face of e dielectric is \(\sigma /2\epsilon (1+1/k)\).The charge on the face is \(\sigma (1-1/k)\)(on!y magnitude).Thus thethe pressure is \(b=\sigma^2 /2\epsilon (1-1/k^2)\)(for the limiting case).Again \(\sigma =CV/A=k\epsilon V/d\).Plugging in the prev exp gives \[b=V^2\epsilon /2d(k^2-1)\]Thus \(V^2=\alpha b/(k^2-1)\).....Although I think if not completely filled then the dependence will be on C specifically(and thus \(t,k\) – Spandan Senapati · 3 months, 3 weeks ago

@Aniswar S K – It would be better with a diagram. But I don't see what thickness means here. Anyways we begin by noticing that when the plates of a capacitor are displaced then the capacitance of the system is given by \(A\epsilon/d.\)where \(A\) is the projected common area.So Here \(A=L(L-x)\) . Now \(C=kL(L-x) /d\). Force by the other charges on this plate is \( F=-dU/dx\). \(U=Q^2/2C\).Note that the charge remains the same but \(\sigma\) changes..Using this you get \(ma=-kQ^2d/2m\epsilon L^3.\) Now that we have acceleration as negative means it's gonna come back to its natural position, overshoot and head to an amplitude, return back. So \(t=4\sqrt (2x/a)\) The constant \(4\) for in one complete cycle it covers\( 4x\) distance.So this yields\[ t=8L/Q\sqrt (mk\epsilon Lx/d) \] .I used d as the distance between the plates. God knows how it's the thickness. Lol. Got It? And the thing wrong in the previous solution was the expression for capacitance... – Spandan Senapati · 4 months ago

@Aniswar S K – I am sorry. It's incorrect. Didn't notice that the dielectric has thickness much smaller than the edge length.... – Spandan Senapati · 4 months ago

@Aniswar S K – Try this way let an external agent displace the upper plate by a distance X then \[W(agent) +W(capacitor) =0\] .Since for an isolated system in the absence of dissipation forces the energy remains conserved. Now since electric force is conservative \(W(capacitor) =-dU\) Where the second term represents the change in potential energy. Since no external potential is applied\( U=Q^2/2C\).Now when we displace the plates by \(x\) say then \( U=L^2\epsilon /\sqrt d^2+x^2\).Now put that in the equation \(F=dU/dx\). and terms of the order \(x^2\) can be neglected. This gives \(F=\psi x\). But we don't have any agent performing so the force applied by other charges on this is \(f=-F\). So the plate exhibits SHM.Find \(T=2\pi /\omega\) – Spandan Senapati · 4 months ago

@Aniswar S K – Us the answer.\(.T=2\pi L/Q(2m\epsilon kd) ^(0.5)\).I solved using energy conservation as there would be fringing fields here and directly calculation of the force may be difficult.... – Spandan Senapati · 4 months ago

@Aniswar S K – Thanks let me try. – Spandan Senapati · 4 months ago

@Prakhar Bindal – ghanta mushkil tha :P agar 5-6 number grace de di to mere to 100 paar jayenge number :P balki set-3 tha sabse mushkil maine saare set dekhe the haina bhai ? tere kitne aajenge btade bhai plz ? – Brilliant Member · 6 months, 1 week ago

@Aniswar S K – I am getting a non integral answer, I used energy conservation and the fact that since string is inextensible,velocity along them would reduce to zero though I may be wrong. – Harsh Shrivastava · 6 months, 1 week ago

@Harsh Shrivastava – Ya.I checked the key it's so incorrect....Maths in a matrix I got-4(Hyperbola)The physics is wrong as well.Esp the first 2 questions.....(Now as per the incorrect key I got (33+25+57).Don't know but in maths the coefficient of(term independent of x is given wrong)...And they also gave that meso compound one wrong.Seriously I hate fiitjee exams for their incorrect answer keys..... – Spandan Senapati · 6 months, 2 weeks ago

@Harsh Shrivastava – We have a screwed up schedule here.I told you.Here they conduct exams from 6-9pm and they don't put the answer keys even.How did you get the answer keys......I will be telling tomorrow. – Spandan Senapati · 6 months, 2 weeks ago

@Spandan Senapati – I was the last one to be interviewed so they asked me easy questions.

First they asked me C1+C2+C3+C4+....Cn prove this in two ways.

Then they asked a multinomial type question .

Then an easy physics question was asked.

Then some easy electrophilic addition question was asked.

That's all.Best of luck! – Harsh Shrivastava · 7 months, 1 week ago

@Harsh Shrivastava – Nothing is difficult in this whole world ... stop thinking about that and let the studies keep going... – Aniket Sanghi · 7 months, 2 weeks ago

@Harsh Shrivastava – I Would not say difficult (class 12) just its a bit bigger than class 11 in terms of syllabus . but class 12 mostly has 55-60% weightage in JEE So you can understand its importance. – Prakhar Bindal · 7 months, 2 weeks ago

@Aniswar S K – Hey looks like you qualified nsec.from your discussion.this is indeed a grt achievement considering the fact that you are in 11.which state and about your kvpy(when is it) – Spandan Senapati · 7 months, 3 weeks ago

@Aniswar S K – Mine is 14/2 =7th rank – Spandan Senapati · 7 months, 3 weeks ago

@Prakhar Bindal – Thnx! – Harsh Shrivastava · 7 months, 4 weeks ago

@Aniket Sanghi – will bio question would be asked to a pcm student – Piyush Kumar Behera · 9 months ago

@Aniket Sanghi – Thanx for your suggestions.will they be asking questions from all the 4 subjects. – Spandan Senapati · 9 months ago

@Aniswar S K – Sorry bro I don't have image. – Harsh Shrivastava · 2 months, 2 weeks ago

@Harsh Shrivastava – HownHow much in P,C,M? – Spandan Senapati · 2 months, 2 weeks ago

@Harsh Shrivastava – Me scoring 222 as per this key.I guess the following answers are incorrect 1)Maths-f(x)=x^3/9.So x=+-3.2)Phy-Current through DE is zero right?Or am I fooling myself.And that matrix on potential energy x<x(2).that's incorrect.It can't be right?. – Spandan Senapati · 2 months, 2 weeks ago

@Sayantan Saha – Mine is Physical education.I had taken Biology in the initials of class-11 but I changed to physical edu.Taking PCMB is quite a strenuous job and when your target is IIT based there is no point in choosing biology.it just adds to pressure. – Spandan Senapati · 2 months, 3 weeks ago

@Aniswar S K – And to the other problem on dielectric I will just add a general approach.We shall again make use of Ohms law \(J=\sigma E\).Initial charges can be found out easily \(C=A\epsilon k/(k+1)d\).Thus charge on plates of capacitor \(Q*=CV\) and that on plates of dielectric is \(Q*(1-1/k)\).Let's say we are asked the general equation of current at any time 't'.As usual let \(Q\) be charge on capacitor plates and \(q\) on dielectric(this won't be equal to \(Q(1-1/k)\) coz Resistance comes to play now.).So \((2Q+q)/A\epsilon d=V\).And from ohms law in dielectric \[J=-(dq/dt)/A.=\sigma (Q+q)/A\epsilon d\].From the first eq express \(Q\)in teams of \(q\) and set it in the second eq.You get time constant of the circuit as \(\tau =2\epsilon /\sigma =2\rho \epsilon \).Now you can get what's being asked.Although the eq of current was nt necessary its just formal. – Spandan Senapati · 2 months, 3 weeks ago

@Aniswar S K – To start with the first problem.On Resistivity.It makes use of ohms law \(E=\rho j\).And so its evident that \(dV=\rho j.dl\).Here the second term is a dot product.Now choose 2 orthogonal set of directions.Here they are the directions in which \(\rho (min)\) and \(\rho (max)\) or (X axis)are oriented. Use Ohms law in this 2 directions.Its just a hint.Try this way you get something like \(\delta V=bV(\rho -\sigma )(sin2\theta )/2l(\rho (sin\theta )^2+\sigma (cos\theta )^2)\).Note that here \(\rho \) and \(\sigma \) stand for maximum and minimum resistivity – Spandan Senapati · 2 months, 4 weeks ago

@Aniswar S K – Nice questions, from which book are they? – Harsh Shrivastava · 2 months, 4 weeks ago

@Prakhar Bindal – Can't comment since no major test has occurd but better than class 11 :P – Harsh Shrivastava · 3 months, 3 weeks ago

@Prakhar Bindal – Nice. I am still fascinated by the Olympiad world especially when spandan Senapati is posting about debaditya. Iam yet to go into complete jee mode!! – Aniswar S K · 3 months, 3 weeks ago

@Prakhar Bindal – Fine...I am more focused now.I really didn't take jee that seriously in class 11. – Spandan Senapati · 3 months, 3 weeks ago

@Prakhar Bindal – Good for now. Finally I have learnt to manage my time well during exam and also I have developed an interest for chemistry . – A E · 3 months, 3 weeks ago

@Prakhar Bindal – Awesome!

Enjoy!

Btw our school topper is going mit this year. – Harsh Shrivastava · 3 months, 3 weeks ago

@Prakhar Bindal – congratzz bro ! ..... – Sanyam Goel · 3 months, 3 weeks ago

@Prakhar Bindal – Nice....and congrats a lot.....All the best. – Spandan Senapati · 3 months, 3 weeks ago

@Prakhar Bindal – Nice...Congrats a lot.I don't know how much our school topper has but anyway of our hper result isn't good then its a bad omen for us....We will have to study in hper period that's the worst thing.Just to make clear we have 6 periods a week and our teacher doesn't come abt 5 times.He is very busy.....so its usually a bunk period for us. – Spandan Senapati · 3 months, 3 weeks ago

@Aniswar S K – Ya I solved it.You get \(V=(kd+(1-k)t)√2b/(k^2-1)\).I have added the solution for a completely filled capacitor but when thickness is given just replace \(C=C(eq)\),and those 2 capacitors are in series. – Spandan Senapati · 3 months, 3 weeks ago

@Aniswar S K – Thanks bro for problems! :D

Keep posting more! I'll also post some! – Harsh Shrivastava · 4 months ago

@Aniswar S K – What are the other parameters mentioned.....Like radius,charge on the ball etc. – Spandan Senapati · 4 months, 1 week ago

@Aniswar S K – For us even function is not over!!!!

BTW I guess there is an acute shortage of diferrential calculus problems ! – Harsh Shrivastava · 4 months, 1 week ago

@Aniswar S K – For us definite integration is over.So I solve integration ones from Ronak aggarwals feed.Differential calculus I too want some good source.I think harsh can help us better.some questions from ronaks feed are quite tough.do try them. – Spandan Senapati · 4 months, 1 week ago

@Aniswar S K – No dont I have .I don't know ifits available.But you can post them here . – Spandan Senapati · 4 months, 1 week ago

@Aniswar S K – Like David morin's book solution or answers to exercises are unavailable.But you can post the questions here if you have any doubt. – A E · 4 months, 1 week ago

@Aniswar S K – You probably didn't get the statement right perhaps.It means that the outer part is shielded from the inner.Means that the field due to the induced charges(here it means charges induced in the under surface not on the outer ones)+point charge is zero outside the vicinity of the conductor.Like take a very simple ex a point charge is placed at the centre of a spherical conductor then -q would be induced on the inner one and +q(if neutral on the outer one).Then the field due to -q(on the inner surface) and +q(point charge ) is quite clear to be zero for outside points(r>R).A similar argument says that the inner part is shielded from the outer.It means that the field at (r<R) is independent of the charges induced on the outer surface.Got it? – Spandan Senapati · 4 months, 2 weeks ago

@Spandan Senapati – How many tests in FIITJEE do you guys have? We have our first coming Monday and will probably have one in every 2 week.

@Spandan Senapati @A E @Aniswar S K – Harsh Shrivastava · 4 months, 2 weeks ago

@Spandan Senapati – Oh I solved that long ago.Nice problem.H ow did you solved? I used Fermat point.

Whenever it comes for finding minimum distance inside triangle go for Fermat point. It is the point from where sum of distances to the sides is minimum. And here construct triangle with sides (0,0);(0,5);(12,0) and then find Fermat point which is the point such that <APB = <......=120°. I had a PDF which provided an awesome proof of it. – Harsh Shrivastava · 4 months, 2 weeks ago

@Spandan Senapati – @Spandan Senapati do you know sarthak behra's marks? I got 69 in apt and 96.14 in interview – Prathyush Poduval · 5 months ago

@Spandan Senapati – Well congrats a pretty high score in interivew. – Prakhar Bindal · 5 months, 1 week ago

@Spandan Senapati – Awesome bro!

I got 52.5 in aptitude and 63.2 in interview thus overall 54.99 (😢) if only I had one mark more... – Harsh Shrivastava · 5 months, 1 week ago

@Harsh Shrivastava – If that were to happen even then in symmetric distributions the net charge must be sigmaArea(for planar surface of course)If it induces charge On a certain surface then on any other it must be q and summing all these gives q.But unlike a spherical symmetry where the induction of charge would be symmetric the system given here might have different densities at diff point(if consider induction)and may be calculating the force becomes tedious by integration.So again physics is all assumptions that you make.For a sphere although using Image Charges is the most apparent way. – Spandan Senapati · 5 months, 2 weeks ago

@Spandan Senapati – We didn't had any.

How was the paper? tougher than previous? – Harsh Shrivastava · 5 months, 3 weeks ago

@Aniswar S K – Hope to do so. – A E · 5 months, 3 weeks ago

@Harsh Shrivastava – No problem...Just chill...Better luck next time.SX is still there..No rejoicing for me as well.Have another reshuffling test on Sunday. – Spandan Senapati · 5 months, 3 weeks ago

@Aniswar S K – Congrats to you as well...air 119 is great as well.You will come for Vijyoshi?? – Spandan Senapati · 5 months, 3 weeks ago

@Spandan Senapati – How much are you scoring, if you want answer keys, you may check Fiitjee Bhilai microsite, click on batch formation test result link and then proceed. – Harsh Shrivastava · 5 months, 3 weeks ago

@Spandan Senapati – Yeah we too had that paper. – Harsh Shrivastava · 5 months, 3 weeks ago

@Aniswar S K – My friend told that his father had called kvpy office and they told its most probably to come out on 2nd April...Delay is a bit clear to me as in our interviews they had not collected the mark sheet.Some had to send them later(including me)...So abt a week or so to go.... – Spandan Senapati · 6 months ago

@Harsh Shrivastava – My views are

Algebra- AWESOME Simply awesome you can't get a better book than this

Coordinate geometry- too easy . definitely not of advanced level (especially conics straight lines and circles are too good but conics sucks in this book)

Calculus - Not too good . Arihant is too better

Vector 3D- Personally not tried it – Prakhar Bindal · 6 months ago

@Prakhar Bindal – It was good . I Cant say about marks at all . Semiconductors was a bit bad . expecting for the best . 2nd april is a big day JEE Mains!! – Prakhar Bindal · 6 months, 1 week ago

@Prakhar Bindal – acha bhai bye , meri physics hi thik h math me fatti pdi h pre-bord me 60 no. the , uski tyari krni h atleast 90-95 ke aas-ps to phuch hi jaoonga padke jauhga too.. best of luck bro – Brilliant Member · 6 months, 1 week ago

@Prakhar Bindal – thik ti yaar aimed for 100, itni zabardast tyari ti , fir bi 95-98 aage to mei bhut khush hu , teri ? – Brilliant Member · 6 months, 1 week ago

@Aniswar S K – No problem.Take your time and if you do by force method it will be good as well..That is indeed a tough fluid mech question..... – Spandan Senapati · 6 months, 1 week ago

@Aniswar S K – You can refer the book by AP French(MIT Introductory Physics Course). – Spandan Senapati · 6 months, 1 week ago

@Aniswar S K – And in systems as such its better to make use of energy conservation..And this question needs some more thinking.Let me give some hints(1-Eq of continuity 2)Co amputation of potential and kinetic energy of system(integrals).Force method is useful in systems where you are able to predict the behaviour of forces,their magnitudes etc.And here it will be quite apparent that analysing forces isn't quite easy.... – Spandan Senapati · 6 months, 1 week ago

@Aniswar S K – That's a upper bound that you can restrict the ration to be.But we need the best bounds.And that won't be possible for this process must be accompanied by some net heat exchange(Or else just a sort of ideal process.Violation of 2nd law). – Spandan Senapati · 6 months, 1 week ago

@Aniswar S K – I think it is correct.What are you getting? – Harsh Shrivastava · 6 months, 1 week ago

@Harsh Shrivastava – What did you mean by best bound? – Spandan Senapati · 6 months, 1 week ago

@Aniswar S K – Hey there is a thing that the piston is nt massless so Weca t equate the forces perhaps. – Spandan Senapati · 6 months, 1 week ago