@JohnRennie Hi!

Hi :-)

@JohnRennie Are you free?

Yes

@Wolgwang Hello ?

@JohnRennie I want your opinion on something. How to upload a .pdf on your server?

swarchive.ratsauce.co.uk/.uploads ?

Use swarchive.ratsauce.co.uk/.uploads

@JohnRennie Should I remove the highlighted part from Q-88 on page 3?

Got it.

(Context is on page 1)

I am asking because I am presuming that...

I don't have a strong view on it ... I guess it is not important to your objection so I'd probably remove it.

@JohnRennie Ok. In q-89 on page 4, I have provided two reasonings. Should I remove one of them?

No, you can leave both thre.

@JohnRennie Is it fine to quote doi link of an article? or should I attach the pdf of that document?

I wouldn't attach a pdf as that just clutters up the inbox of whoever is handling the mail. Quoting the doi should be fine.

@JohnRennie I have uploaded an image on your server.

What am I supposed to write in the feedback box? The same thing I wrote in that pdf?

Ah, OK, so it does allow you to upload pdfs.

My guess is that the reviewer will read the info from the feedback box and only read the pdfs if the stuff in the feedback box looks convincing.

Ok. Thanks :-)

So you need the text in the feedback box to make clear what is wrong and why the reviewer needs to open the pdfs.

Ohk

Hello @JohnRennie sir

Sir I kno about

Splitting of conduction and valence band

But i didnt get why on increasing temperature

The electron can travel

Across the entire crystal

In principle the electrons in the bands of a crystal behave like free particles rattling around in a box.

Ok

That's because the de Broglie wavelength of the electrons is much larger than the spacing between atoms, so the electrons don't scatter off the atoms.

Ok

It's the same reason light can travel through a (transparent) crystal. The wavelength of the light is much greater than the size of the atoms so the light doesn't scatter off the atoms.

Ok....

Sir are you here?

Yes, but I didn't think there is anything more to say ...

Why this occurs in conduction band only

Bot in valence band

The electrons are free in the valence band as well, but you cannot get a current in the valence band for reasons that are a bit subtle.

Then i am done then

Suppose we approximate the electrons as moving freely in a box, then the electrons states are like the states for a particle in a box.

@PrateekMourya OK, I was going to explain why we can't get a current in the valence band. Do you want to go through this?

I have less time

Like 5 mins

OK. Bye then :-)

After that

I have to submit my ohone

Can you explain after 9 pm tonight

oh can i ask a doubt?

Yes, I'll be around. Though it isn't something you need to know for JEE.

Ok

We should only spend time on it if you're interested for personal reasons.

Otherwise just accept it.

I will just accept

OK :-)

Can i ask now sir, or later?

Ask now

Why is it that the magnetic field at the centre of a circular loop is $\mu/2$ times $NI/R$, where N is the no of turns, but for a solenoid, it is $\mu.n.I$, where n is the no of turns per unit length?

is it because in the derivation for the magnetic field at the center of a solenoid, we assume the solenoid is so tightly packed that its like a cylinder?

Take a simple case of N = 2

yes

Then for the loop we have two single loops superimposed, and their fields will just add. So the field from 2 loops is just twice the field from a single loop.

yess

But now let's turn this into a kind of solenoid by separating the two loops by some distance d.

yes

The field along the axis of the loops falls off with distance along the axis (I forget the exact equation, but it doesn't matter anyway).

yes

So the field at the centre of one loop is now the field from that loop plus an amount from the other loop that is slightly less than the field at the centre of the other loop.

So the field along the axis of a solenoid is clearly going to be different from the field at the centre of a loop with n turns.

You could imagine taking your loop of N turns and separating out each turn along the axis by some distance d, then you'd have a solenoid with 1/d turns per unit length.

The field at the centre of the middle loop would then be some complicated sum of the fields from all the other loops.

I must admit it isn't obvious to me how this sums up to the simple expression for the field in a solenoid, but presumably it does.

so the difference is because of the separation?

Yes. The separation matters becaue the field along the axis of a single loop decreases with distance.

oh makes sense

thank you sir

:-)

@napstablook yeah i knew it, anyways Thanks !!