« first day (1015 days earlier)   

5:34 AM
@JohnRennie Good Morning sir :-)
 
@JohnRennie Hi
 
Morning :-)
 
@JohnRennie hello sir...are you busy now?
@JohnRennie I want to ask you a question...
 
@user8718165 no, though Aladdin is about to ask me about Python ...
@user8718165 ask now! :-)
 
@JohnRennie okay sir, how does an electron move sir? We discussed that its just a probability cloud...
@JohnRennie Is it really a little ball or a wave physically or does it change its physical appearance from time to time sir?
 
5:41 AM
There are two separate questions there.
 
@JohnRennie okay sir
 
Which one do you want to discuss first?
 
@JohnRennie sir first one please :-)
 
OK. The electron is indeed (in general) a fuzzy object like a cloud. But why should that cause problems with it moving?
Consider this thought experiment.
 
@JohnRennie okay sir
 
5:44 AM
Take a stationary (fuzzy) electron, and zoom past it at some speed $v$. In the electron's frame it is at rest and you are zooming past at $v$, but in your frame you are at rest and the electron is moving at $-v$.
 
@JohnRennie yeah sir
 
So in your frame we have a fuzzy electron that is moving.
 
@JohnRennie yeah sir
 
So there is nothing special about fuzzy cloudlike objects moving.
 
@JohnRennie okay sir...another question on this thing?
 
5:49 AM
Yes?
 
@JohnRennie is it that the cloud is moving so fast around the atom we think it's a cloud surrounding the atom at all times...?
 
No. The cloud isn't moving at all in the classical sense.
 
@JohnRennie :/ why sir?
 
why isn't a useful question. Quantum objects are fundamentally different from what we think of as classical objects. They are always spread out (delocalised is the technical term) so they do not have a single position.
That's just the way it is.
 
@JohnRennie yeah sir...got it...So don't they move around the atom at high speed?
@JohnRennie okay sir
 
5:55 AM
@user8718165 no, they are not pointlike objects moving round the atom at high speed.
The angular momentum of the 1s electron is zero.
 
@JohnRennie okay sir...got it
 
When you say why do books write it that way I assume you're thinking about the Bohr model.
The Bohr model is wrong, and I don't know why it's still taught. It just confuses students.
Students often try to approach QM by starting with a classical approach and trying to see what changes when you move to QM, but this is not a good way to do it. QM is fundamentally different from classical mechanics.
 
@JohnRennie that statement is indeed written in Bohr's model and nowhere else :-)
@JohnRennie Got it sir....
 
I think the JEE syllabus includes the Bohr model so you have to learn it. But it isn't useful for understanding QM.
 
6:18 AM
@JohnRennie hi Alesha here.
 
@yuvrajsingh hi :-)
 
I have question regarding astronomical telescope.
@JohnRennie
 
OK. I don't knw a lot about telescopes, but I'll help if I can.
 
OK, sir I read about telescope their are to piece eye piece and objective piece.
So my class notes says that, objective focal length is greater than eye piece focal length.
@JohnRennie
Why.
Can you explain sir @JohnRennie
 
@yuvrajsingh I'll have to Google to remind myself how telescopes work ...
 
6:25 AM
OK.
 
6:41 AM
@JohnRennie yes sir....
 
@yuvrajsingh Suppose you are trying to look at something small, you use a magnifying glass. Yes?
That is you hold the magnifying glass to your eye and when you look at the small object you see it magnified.
 
@JohnRennie OK.
 
This is what the eyepiece of the telescope does. The lens at the far end creates an image of the object you are looking at, and the eyepiece then magnifies that image just like holding a magnifying glass up to your eye.
You want the eyepiece to have a high magnification, i.e. like a powerful magnifying glass, so you want it to have a short focal langth. Yes?
 
Ah, OK, so more the focal length, higher the converging power of objective lens.
So sir first is real. And second image is imaginary.
 
What's complicated about the telescope is that the lens in your eye is an integral part of the optics.
That is, the telescope on its own does not create an image. It requires the lens in your eye as well.
 
6:52 AM
Can you confirm my second last comment. @JohnRennie
 
@yuvrajsingh The objective lens creates a real image inside the telescope, then the eyepiece creates a virtual image of the real image. Finally your eye creates a real image of the virtual image on your retina.
 
OK, sir thanks, If you can do one more favor to me.
@JohnRennie
 
Yes?
 
Can you help me in understanding the magnification formula.
 
$M = v/u $ ?
 
7:29 AM
No for telescope. @JohnRennie
 
To be honest I don't know how to calculate the magnification for Keplerian telescope.
 
OK sir.
 
I think the magnification is the ratio of the objective focal length to the eyepiece focal length, but I don't know how to derive this.
 
Yes you are right sir, I am struggling with some triangle. Sides ratio.
 
8:19 AM
@JohnRennie hello sir
@JohnRennie are you working now? :-)
 
@user8718165 yes, I need to work now for about half an hour - maybe up to an hour depending on how it goes. Try me again around 14:30 your time.
 
@JohnRennie okay sir....peace :) Please ping me when you're finished :)
 
9:07 AM
@user8718165 hi, I've finished work now.
 
@JohnRennie are you busy sir, I have a question.
Alesha here.
 
@yuvrajsingh I've finished work now and I'm just drinking coffee and staring out of the window :-) So nowis a good time to ask.
 
Do you know how to read Vernier scales?
 
Yes.
Sir I want a favor from you.
 
9:19 AM
So the reading on the top diagram is easy isn't it?
@yuvrajsingh yes?
 
Actually I asked this question, because I have little misconception regarding vernier caliper.
 
OK ...
 
Vernier caliper allow, us to measure the something less than 1mm right sirm
 
Yes
 
So when is say 10 division of main scale align with 9 division of vernier scale., it mean one vernier division 10/9
 
9:23 AM
Yes
 
,ok,so today I was in physics lab, and our sir given this question to us.
 
But how do I do it practically.
 
@yuvrajsingh This question?
 
Yes, but I do not know how do I measure the value.
If you can, explain how do I see the value.
@JohnRennie
 
9:34 AM
With Vernier scales you very quickly get to understand them intuitively, so at a glance I can see the upper scale is 2.87 and the lower 2.83. But until you get used to them I can show you how I would approach them. This does not necessarily match what your book will say. Shall I go ahead and say how I would do it?
 
Yes sir.
 
@yuvrajsingh Let's start with the top diagram. The text tells that 10 Vernier divisions = 9 main divisions, so each Vernier division is 0.9mm. Yes?
 
The two scales match where I have drawn the red line. This is at 7 on the Vernier scale and 35mm on the main scale. (I've just realised I mislabelled it as 3.5mm - sorry)
 
Yes.
35+6.3mm will be the final reading sir.
 
9:42 AM
So suppose we start at the red line, i.e. at 3.5cm, and move backwards to the zero on the Vernier scale. That is, we move back the distance shown by the blue arrow. This takes us to the reading.
So the reading is 3.5cm - 7 x 0.09cm = 2.87cm
@yuvrajsingh minus not plus
 
Sir why.
Why we move toward the zero point.
 
Let me update my diagram to explain ...
The green arrow starts at zero (off the left side of the diagram) and ends at the reading.
So the length of the green arrow, which I've called $x$, is the reading we want. Yes?
 
OK, one last why we minus the vernier scale reading.
 
@yuvrajsingh Let's call the Vernier reading $y$, where $y$ is the length of the blue arrow. Then $x + y = 3.50cm$. Yes?
 
9:53 AM
That means $x = 3.50cm - y$
Which in this case means $x = 3.50 - (7 \times 0.9)$
 
OK sir got it.
One more question.
@JohnRennie
 
@yuvrajsingh yes?
Do you want to go through the second scale as well?
 
Regarding screw gauge.
 
@yuvrajsingh yes?
 
No sir, that would be simple sir it I am right 10/11 multiply 7.
Would be vernier scale.
 
9:58 AM
This time the Vernier divisions are 0.11cm, so the length of the blue arrow is $y = 7 \times 0.11 = 0.77$
 
Sorry I typed wrong.
Actually while calculating. Reading in screw gauge.
We use a term pitch.
 
OK ...
 
Sir, in one cycle it move.
A distance d.
 
Yes, typically the screw gauge is designed so one complete revolution moves one division on the main scale.
Or sometimes half a main division.
 
But let say I have to calculate diameter of pipe. How would I measure it.
 
10:07 AM
@yuvrajsingh I'm not sure what you are asking. You mean how to make a measurement with a screw gauge?
 
@JohnRennie hello sir...sorry I couldn't reply. I'm in class. Can we talk later sir :-)
 
@user8718165 I'm around for another couple of hours. Until 12:30 UK time - 18:00 Indian time.
@yuvrajsingh do you want me to find a picture of a screw gauge to use as an example, or have you got a picture you want to use?
 
@JohnRennie okay sir :( Then I'll have to ask you tomorrow.
 
You can sir
 
10:12 AM
@user8718165 I'll be around tomorrow as usual.
 
@JohnRennie okay sir...thank you very much. :-)
 
@yuvrajsingh give me a moment to find a picture.
@yuvrajsingh there, that's an image I found by Googling. We can use that as an example.
 
Each complete rotation of the screw moves one division on the main scale, and one division on this main scale is 0.05cm.
OK so far?
 
How do we calculated this one division.
@JohnRennie
 
10:24 AM
Actually there isn't a simple way to tell because it depends on how the gauge has been designed. With a real gauge you just turn the screw one complete turn and see how much it moves along the main scale.
In questions the question will normally tell you what the main scale division is.
 
OK sir continue.
 
So we know that if we turn the screw one complete turn the main scale changes by 0.05cm.
So if we turn the screw by half a complete turn the main scale changes by 0.025cm
If we turn the screw one tenth of a turn the main scale changes by 0.005cm.
OK so far?
 
OK, well the scale on the screw just tells us what fraction of a turn we have rotated the screw.
In this case the scale on the screw goes from zero to 50 as we go right round the screw.
So suppose we start at zero and rotate the screw until it reads 25, then we must have turned it half a turn, because 25 is half of 50.
 
10:33 AM
@JohnRennie Hi :)
 
@KevinN hi
@yuvrajsingh Now look at the diagram:
 
I'm on my phone, so I don't think we can continue our previous discussion anytime soon. But I got a quick question! :)
 
@yuvrajsingh On the main scale we are just past 0.55cm. Yes?
 
Yes.
 
@KevinN you can post the question, but we need to finish the vernier question first
 
10:36 AM
@JohnRennie Sure:)
 
@yuvrajsingh the gauge is designed so that the screw shows zero when it is exactly lined up with a main division. So when the main gauge was at exactly 0.55cm the screw gauge would have shown zero.
So the question is how far past zero have we turned the screw gauge.
And looking at the scale on the screw gauge it reads 12. Yes?
 
@yuvrajsingh So the fraction of one rotation we have turned the screw gauge is 12/50. Yes?
 
OK.
Yes sirm
 
And we we know one complete rotation of the screw gauge moves 0.05cm on the main gauge. So 12/50 of a rotation moves a distance $x$ along the main gauge where $x = 0.05cm \times 12/50$. Yes?
 
10:41 AM
Yes sir.
 
So $x = 0.012cm$
That is, we started at 0.550cm on the main gauge and moved an additional distance 0.012cm.
@yuvrajsingh OK?
 
Yes sir.
 
So the total distance is 0.550 + 0.012 = 0.562cm
And that's how you read a screw gauge.
 
Got it sir.
 
@JohnRennie I read somewhere, just now, that Black Marlins secrete an oil-like substance from a special gland on its skin. It is suspected that this oil might have reduced the drag when it swims. I don't really find this intuitive or at least right now. I mean I know why oil makes the floor slippery, but what about sea water? Aren't they both liquids, in a sense that the water molecules could already move 'freely' , so how does oil play a role here?
 
10:45 AM
What kind of things we measure in it
 
@yuvrajsingh you can use a screw gauge to measure anything you want.
@KevinN I would guess the oil just smoothes out the skin.
The fish skin is probably slightly rough due to irregularities on the scales. If the oil is thick and gooey it will spread out to form a smooth film and help remove the irregularities.
 
@JohnRennie Aah. I can see how that's possible
 
@JohnRennie bye sir. See you later.
 
@yuvrajsingh bye :-)
@KevinN it's just a guess. The only marlin I have seen were on a plate :-)
 
@JohnRennie Hahaha, me too ;)
When you have a lot of bumps in an object, and is moving through water, how exactly does that increase drag. I would suspect that it increases the surface area and more water molecules would start 'bumping' ?
 
10:51 AM
@KevinN it causes turbulence
 
@JohnRennie What exactly is turbulence?
 
@KevinN that's a long discussion. You need to Google it.
 
@JohnRennie Ya, right :)
Basically, more bumps and imperfections, more turbulence?
 
@KevinN yes
 
@JohnRennie I heard that you're a fan of computers?
 
11:00 AM
@KevinN I am a big time computer nerd :-)
 
@JohnRennie More into software or hardware?
 
@KevinN both
 
@JohnRennie You're still updated on current's release yea?
My laptop is a piece of junk and tired of continously resetting it. Any recommendations?
 
What model is your laptop? i.e. what manufacturer? Dell? HP? Samsung? And what is the model number?
 
A $600-800 would be ideal
Oh goshh :) I'm on the go now. One thing I know that it's quite an old one. Let me find and send you an image of it.
 
11:09 AM
OK ...
 
@KevinN an HP?
 
An Hp r202 tx if I'm not mistaken
There were a few models but it was on that subcategory
 
2Gb of ram, but upgraded it into a 10. An i5 and a horrendous 820m GPU
 
11:13 AM
Which i5?
The link I posted shows an i3-4005U
 
It must've been a different model but the exterior was identical
 
@KevinN Well if you replace the crappy old mechanical disk by an SSD and bump the RAM to 8GB that will be a nice fast laptop. Both of those you can o yourself in 15 minutes.
 
Mines a 10GB already
There's no way I'm sticking with a 2 :(
 
Do a new clean install of Windows 10 - this is free from Microsoft - and you'll have a nice fast laptop.
 
You could replace the HDD to an SSD? Is that even possible?
 
11:17 AM
A 256GB SSD will cost you less than $50. I forget how much they cost these days. Probably a lot less than 50 dollars.
 
Aren't most laptops fixed?
(except ram occasionally)
 
@KevinN yes. It's a straightforward swap. Take off the base plate, unscrew the old disk, screw in an SSD and away to go.
 
Isn't an SSD much smaller than an HDD?
@JohnRennie You can answer @yh05 's question first. He's off waiting :)
 
Laptop disks are 2.5". The latest laptops use NVMe SSDs, and they wouldn't fit, but you can buy 2.5" SSDs that would be a drop-in replacement.
@yh05 hi :-) You need to ask that in the main chat room. Do you want me to move your post to that room?
 
@JohnRennie It says access denied :)
 
11:24 AM
Huh?
 
Sure
 
@KevinN that's a UK retailer and I suppose it might be blocking access from outside the UK.
2 messages moved to The h Bar
 
I suppose. But that works for all kinds of laptops does it?
 
@yh05 OK, I've moved them now.
@KevinN it works for everything that uses a mechanical 2.5" drive. 2.5" SSDs and 2.5" mechanical drives are completely interchangeable.
So the point is that for not much money you can really speed up the laptop.
And a new clean install of Windows 10 will be much more stable and reliable. And it's free.
 
I just reinstalled yesterday :)
 
11:29 AM
A clean install? As in completely wipe the drive and install from scratch? Or a reinstallation over the existing installation?
 
One issue, again, is that my monitor breaking down, there's a black line across the screen. I mean you get used to it, but it would be a pleasure to my eyes to see that removed.
 
Well if you have 600-800 dollars that will buy you an ass kicking laptop these days! :-)
 
If....
 
So if you're willing to spend the money you'll get a new laptop that is much, MUCH, better than your old one.
 
An SSD would be tolerable for my parents to let me buy one for Christmas. An $800, nope :))
 
11:33 AM
An SSD it is then :-)
Whereabouts are you? In India?
 
@JohnRennie US
 
Just look on amazon.com for a disk. What size do you need? 250GB, 1TB?
 
Amazon is a click away :)
250 might be too small honestly
But would a terabyte would cost me a liver?
 
About $100 I think. Let me look ....
 
I really can't type well in the car, tolerate my wobbly sentences
 
That's not too expensive, really
 
Just over $100. Or 60 bucks for a 500GB disk if you can live with that.
 
But would it be worth it though? I won't be at sticking with that laptop for too long.
 
Until you'v experienced how much faster an SSD will make your laptop you won't believe it!
 
Or could i just move the SSD later on?
 
11:41 AM
It is the single most effective upgrade you can do.
@KevinN you can reuse the SSD, but if you buy a new laptop it will use an NVMe SSD not a 2.5".
2.5" drives are only used where the compatibility with the old mechanical drives is required.
 
NVMe is the narrow one yes?
 
Yes. It's like a drive on a card.
 
How fast does an SSD get really?
 
Unbelievably fast. Like Windows starts in 30 seconds.
 
So SSD plays a bigger role than a RAM in booting up?
I've seen those read and write speeds. Pure insanity
 
11:46 AM
An SSD is the SINGLE MOST EFFECTIVE UPGRADE you can make.
Just watch the disk light next time you boot your laptop and see how it stays on for several minutes while the disk struggles to keep up.
 
For Sure, if things go well, I'm getting one :)
Which one would you prefer? A crap Hard Drive but massive loads of RAM or the other way around?
An SSD with less RAM
 
Other way around - no contest.
 
Really? Never knew an SSD would make such a difference
 
Buy the SSD first and the other upgrades later.
@KevinN I guarantee you won't believe how much faster it makes your laptop.
 
Probably because every games say minimum 8GB of ram and no details on the storage device
 
11:49 AM
(unless your laptop already has an SSD of course)
 
Why are SSDs faster? No moving parts i guess?
 
@KevinN yes.
 
Are you into GPUs?
 
@KevinN not really because I don't game. Unless you game the built in GPU in the Intel CPUs is just fine.
So you're own your own with GPUs :-)
 
I once played GTA V (if u know what it is) on my 820m, and it was barely touching 25 fps, very dreadful
 
11:57 AM
Laptops are not ideal for gaming. There are gaming laptops, but they're expensive.
The sort of laptop you'll get for 600-800 dollars is never going to get high frame rates on the latest games. That's life.
 
It is life :(
 
If you want to game look on eBay for a PC with a decent card. $800 will get you a pretty powerful gaming PC.
Or play on Stadia :-)
 
Are you being sarcastic?:) It has not even been released yet, but the fans are raging out already
It technically needs 5G
 
There has been a lot of criticism of Stadia, but mostly because of the terrible way Google rolled it out. If you can get Stadia working then it appears to be pretty good.
@KevinN I wouldn't try and play it over a mobile link. You need a fibre link eally.
Other companies will be releasing competing services in the next year, so even if Stadia bombs one of the others should make it.
 
Definitely
@JohnRennie Thoughts on 5G's development?
 
12:03 PM
Don't care.
I almost never use mobile data.
There's wifi pretty much everywhere I need to work.
 
Haha, true :)
If 5G takes over, would wifi be faster?
 
Anyhow, let me know what you decide. I'll be interested to hear if you do try using an SSD and if so how you get on.
 
I said if things go well.... ;)
But I'm really hoping
 
If you can live with a 250GB SSD that's so cheap surely your parents would spring for it?
Yes it's a bit tight on space, but you can always use the old mechanical drive as an external drive.
 
Yes!
Are you sure it'll be compatible?
 
12:07 PM
But before you buy check the exact model of your laptop and download the service manual to see ow easy it is to swap the disk.
 
I hope my mom didn't throw the manual :)
 
If you want I can have a look. You just need to give me the exact model nuber off the baseplate on the laptop.
@KevinN you'll need to download the manual. I can find the link for you, but you need the exact model number.
Ping me when you're sat at the laptop.
 
Sure. Bye :)
 
Bye
 
 
5 hours later…
4:41 PM
@KevinN hi
 
4:52 PM
@JohnRennie uv here are you busy m
 
@yuvrajsingh I'm doing a few bits and pieces, but I can answer a quick question ...
 
@JohnRennie that, s general chat
If you are busy than it, s OK.
 
@yuvrajsingh I haven't really got the time. Sorry. I'll be around tomorrow morning as usual.
 

« first day (1015 days earlier)