Problem Solving Strategies - 2021-10-20

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4:21 AM

@BannedUser See:

17

A: How is frictional force dependent on normal reaction?

You need to start by considering the microscopic origin of the frictional force. In most circumstances surfaces are rough so when to touch two surfaces together they actually only make contact at the highest points on the surfaces. We call these high points asperities, and in the diagram below I...

4:51 AM

Hi

I have something to ask from @satan29

sure

Do u know about IISC

In Bangalore

a bit, yes. My good friend (AIR-5 in advanced!!) Chose IISC-B

So I want to ask that how do one get admission in IISC

The main route is through an exam called KVPY

4:53 AM

I m in 12th class and now I want to pursue my future education in iisc

But KVPY happens in november

And I m still in 12th

So I should give kvpy next year?

you dont want to give it in november?

Yes, because I m still in 12th studying for boards examination

And I want to start doing for entrance after 12th

hmm OK...

And moreover I don't know anything about the admission process, like the form filling and all

Most people I know give KVPY while they are in 11/12 th only. However you can give it after 12th through, theres the KVPY-SB for that although I'm not exactly sure how that works

@SamyakMarathe KVPY website

4:57 AM

Yes SB is for iisc bsc course, thats what i want to give

@satan29 no I meant regarding form filling for iisc college

kvpy.iisc.ernet.in/main/eligibility.htm

@SamyakMarathe ? Worry about that after you clear the exam

But the internet says that we have to fill the form of iisc in february-april

And I have not given kvpy, and i don't know about sx sa or sb

@SamyakMarathe im pretty sure results will be out by then, thats why

So should i give kvpy next year

Do they happen any time except november

5:22 AM

@SamyakMarathe read the info on that link, and on the website

RishiNandha Vanchi

@Anusha Im looking at Electrical

because from what I heard, electrical backed with the right electives I can move on to do physics or maths later if I like

you can get into IISC through mains also , but you need an exceptional rank

RishiNandha Vanchi

If possible Ill be grateful if Sir can share some opinions on which electives may add the most to this matter when we do get the list of ones we get to take :D

and anyone else aware of it too ofcourse

@satan29 yeah AIR 200 in mains is like crazy especially with 4 attempts lol

@RishiNandhaVanchi yeahh

RishiNandha Vanchi

~~and also how annoying mains is~~

Ah I forgot how to strikethrough here, its been long XD

@SamyakMarathe just give at the same time everyone else in ur batch gives no

5:33 AM

user image

RishiNandha Vanchi

this was in my SX iirc

In this questions I don't get proper reason why potential along path 2 is zero ? there are non-conservative fields all around the solenoid

@RishiNandhaVanchi yes it's from kvpy sx

RishiNandha Vanchi

the law they gave is absolute

what law ?

RishiNandha Vanchi

the field all around the solenoid you say, will behave in a way that it cancels just right when you go around a loop and not have any current threaded within

the integral expression they gave for nonconservative induced field

5:36 AM

the expression they gave is the general definition of potential only

RishiNandha Vanchi

oh my bad, anyways, if you've seen faraday's law

yes

RishiNandha Vanchi

potential around a loop = flux'

(with proper sign convention it becomes - flux')

yes , only for induced EF

Suppose you connect points a and b with a resistor to complete the circuit. We can make this resistor arbitrarily large.

5:40 AM

yes then current will flow

Now you have two complete loops, and we can use Faraday's law for the EMF round the loop, and this will be zero for loop 2 because it does not enclose any flux.

OK so far?

yes

but induced electric fields due to the solenoid are also passing through the path 2 right ?

This doesn't depend on the value of the resistor, so we can make the resistor arbitrarily large to approach the open circuit (infinite resistance) between a and b and the EMF round the lopp remains zero.

@YashAgrawal We generally take the approximation that a solenoid has no external field.

I meant that as flux is increasing and if I enclose solenoid within any circle of any radius then , there is some induced electric field there right ?

Yes, but if you integrate round a loop that does not enclose the solenoid the fields round the loop will integrate to zero.

5:46 AM

yes ,but how to prove it , because I guess electric field in the faraday law is only due to the flux changing inside the loop , it doesn't consider electric field due to other external sources

or is it ?

user image

In it , this E is net electric field ?

Faraday's law says for any loop the EMF around the loop is dependent only on d/dt of the flux inside the loop. Any flux outside the loop has no effect.

when we have a circuit with a battery , it doesn't obey ?

A battery uses a chemical reaction to produce an EMF so Faraday's law isn't going to apply to it.

so faraday law is only for induced emf ?

Yes

5:53 AM

So , we could say that Electric field appearing in the faraday law (image above) is the net induced electric field ?

I guess so, though I'm not sure what you mean by that.

I meant the Electric field we are integrating around that loop to get emf , it is the net induced electric field in the space

like the electric field appearing in the gauss law is net electric field

I'm not sure why you are including net. The electric field is just the induced electric field.

I'm including net as , i meant it does not only induced electric field induced due to changing flux inside loop but also due to any flux outside the loop that is changing (like the solenoid in this case )

Ah, OK, you mean the total field due to all fluxes changing everywhere. Then yes I agree.

6:02 AM

Yes , that's what I meant

Although we can write E = E(due to flux inside) + E(due to flux outside) and line integral of E(due to flux outside) around the loop would be zero

Yes

It's clear now , Thanks sir :)

:-)

3 hours later…

9:28 AM

@YashAgrawal Field of view of image? I have only heard about FOV of eye 🤔

you have not heard it in case of plane mirrors ?

there are some pretty common question as someone walking on a railing placed aside a object and mirror and we need to find distance/time upto which image is visible to the man

@YashAgrawal I have only solved FOV questions of plane mirrors :-/

@Wolgwang For you to see the image a ray of light from the object must be able to reach your eye.

That is a ray from the object gets bent by the lens, passes through the point in space where the image is then continues on (in a straight line) until it reaches your eye. Yes?

Yes

I was thinking wrong.

The field of view is the range of positions of your eye where this can happen.

9:35 AM

Ok got it :-)

Sir but in this question aren't rays non paraxial ? so I guess it's wrong to say it passes through 40 cm right to the lens

@YashAgrawal Are you going to give/take KVPY on the upcoming 7th?

Yes

Do you know what type of calculator will be available there?

It's normal calculator

But it's of very little use

9:39 AM

XD I was expecting a scientific calculator.

@YashAgrawal Yes, that's true, but I doubt the question intends you to go into that level of detail :-)

Yes I guess so

@JohnRennie Sir can you suggest a good source for reading about superconductors

10:40 AM

@YashAgrawal I can't I'm afraid. It isn't a subject I've ever studied. But the theory of superconductivity BCS theory is pretty complicated. You normally don't study it until your final year of a physics degree.

If you have basic questions I might be able to answer.

RishiNandha Vanchi

@YashAgrawal If ur asking for jee, then they will give you what you need

Are superconductors even mentioned in the JEE?

RishiNandha Vanchi

there was one comprehension in 2021 paper

they gave the condition, we needed to know nothing

it was simple only

user image

oh, my bad, its not a superconductor

I confused it with a problem in OPhO 2021

2 hours later…

RishiNandha Vanchi

12:35 PM

user image

found it

1:15 PM

hi

I m stuck in a question, if anyone can help

1 hour later…

RishiNandha Vanchi

2:20 PM

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