Problem Solving Strategies

user8718165

4:28 AM

Good morning sir :-) @JohnRennie

John Rennie

@user8718165 morning :-)

Aladdin

5:11 AM

@JohnRennie how hard is c after python

John Rennie

@Aladdin C is very different to Python. I think it's a lot simpler, but then I've been writing it for 40 years.

yuvraj singh

5:27 AM

Morning to all :)

John Rennie

@yuvrajsingh morning :-)

yuvraj singh

Sir does increase in temperature, will create some change in sound wave.

@JohnRennie

yuvraj singh

5:45 AM

@JohnRennie are you busy sir.

John Rennie

@yuvrajsingh hi, sorry I missed your post. I was doing something at work.

yuvraj singh

No issue sir my question.

John Rennie

The speed of sound varies with temperature, so for a given frequency the wavelength will vary.

I think I've gone through this in a question on the main site. Let me have a look.

11

Q: The speed of sound is proportional to the square root of absolute temperature. What happens at extremely high temperatures?

The speed cannot increase unboundedly of course, so what happens?

8

Q: How can the speed of sound increase with an increase in temperature?

I was reading a textbook. I found that it was mentioned the speed of sound increases with increase in temperature. But sound is a mechanical wave, and it travels faster when molecules are closer. But an increase in temperature will draw molecules away from each other, and then accordingly the s...

acoustics textbook-erratum

user8718165

hello @JohnRennie sir

John Rennie

@user8718165 hi

@Malavika hi :-)

user8718165

5:56 AM

@JohnRennie sir will you please have a look at an answer?

John Rennie

@user8718165 post the link, though I need to work now for a few minutes.

user8718165

@JohnRennie please sir...just a while

John Rennie

@user8718165 it looks fine

user8718165

@JohnRennie thank you very much sir :-)

psa

@JohnRennie If you have a bunch of data for, say, current through a diode by measuring the voltage across a resistor and its resistance in series with it... How do you find the error? Do you add the random error (I'm assuming this is the standard deviation, or standard error, one of the two?) and the uncertainty in the multimeter in each case in quadrature or?

yuvraj singh

6:02 AM

@psa According to what I've learnt, in any expression of multiplication or division, the percentage errors of each term are added up to find the equivalent percentage error. That is, if $$y=\frac{\text {AB}}{\text C}$$ then $$\%\;\text{error in y}=\%\;\text{error in A}+\%\;\text{error in B}+\%\;\text{error in C}$$

Do you have any question I can go through it.

yuvraj singh

6:14 AM

@JohnRennie hi can you check my answer.

1

Q: Can the law of the lever be derived from only Newton's Three Laws of Motion?

Can the law of the lever be derived from only Newton's Three Laws of Motion?

newtonian-mechanics torque statics

psa

I understand that, but that's for systematic uncertainty (due to your measurement device), not due to random error.

I mean - take a data set of, say, N = 100 points. How do you find the random error in the data set?

No, no. That's systematic uncertainty again.

Am I just looking for the standard error here to find the random error in the data set? i.e. standard deviation divided by the square root of N?

yuvraj singh

@psa is this example OK. To start. i.stack.imgur.com/3pVLm.png

John Rennie

6:33 AM

@psa Are you using a linear regression to fit a line to the data?

psa

Nope. I'm using a special fit. To be precise, I'm fitting to the function $|I| = |I_{0}||\exp(eV/k_{B}T) - 1|$

It's a fit specifically for that function

John Rennie

There isn't a simple way to get the errors in the fitted variables.

psa

I just want the random error in $|I|$

I'm using that for my error bars in the fit

I have a data set for $|I|$

Well, specifically, I think I'm adding the random error and systematic error in quadrature.

To get the total uncertainty.

John Rennie

Systematic errors can't be estimated from stats. You normally treat them separately.

psa

No I know... I've dealt with those already

But I figured I could add the two in quadrature after I've found them separately to get the total uncertainty

That might be wrong... If so, all I'm really worried about is finding the random error in $|I|$

John Rennie

6:38 AM

For the errors in $I$ you'd normally do the fit then calculate $I_{expt} - I_{fit}$ for each point and then calculate the standard deviation of all the differences. This will give you a guide as to the random error in the measurements of $I$.

psa

So I just need the standard deviation of the residuals?

John Rennie

Yes

psa

I'm slightly confused then... How in the heck do I find the uncertainty in I? It's just the systematic uncertainty in each case?

As in, "the uncertainty of I" = "my error bars in the fit"

John Rennie

Assume the fit is perfect, then for every data point the residual is due to experimental error. Ignore any systematic errors for now, then the residuals will be due to the random error in the measurement of $I$.

So the stdev of the residuals will give you the stdev of the experimental measurements of $I$.

psa

I might be confusing you... Practically speaking, I need to find some "uncertainty in |I|" and put that into a column in my data set (could obviously be different for each row!). Afterwards, using both my data and the "uncertainty in |I|" column, I do the fit.

Is this, on its own, the systematic uncertainty?

Because it sounds like I actually need to do the fit first to get the random error.

And I didn't actually know that before.

Forgive me, I'm honestly terrible at error propagation and statistics. I haven't had any formal training in it so I feel like I'm kind of just doing a hack job of it along the way in an experimental course. Ideally, I actually want to understand what I'm doing with error...

John Rennie

6:50 AM

Normally you'd do the experiment and you'd estimate the experimental error by repeating the same measurement a few times to see how much the measurements vary. I guess in this case you haven't actually done the experiment - you've just been presented with the data.

psa

No, we did the experiment.

John Rennie

So can't you estimate from your experience of doing the experiment what the experimental errors in the intensity are?

psa

I didn't know that's how you'd determine it.

That'd be a really rough estimate, but I suppose.

yuvraj singh

@JohnRennie hi.

psa

I found when I used the systematic uncertainty in the device, the error bars seemed way, way too small.

yuvraj singh

6:56 AM

@JohnRennie if you get please, check my answer I already posted the link.

John Rennie

@yuvrajsingh it looks fine to me :-)

yuvraj singh

Thanks.

Can you up vote, it because in future reference, I someone find not appropriate, I can talk to you. @JohnRennie

yuvraj singh

7:15 AM

@JohnRennie

Hi

John Rennie

@yuvrajsingh something has come up at work ...

yuvraj singh

I am in jaipur right now. @JohnRennie

No issue.

yuvraj singh

7:37 AM

@JohnRennie

John Rennie

@yuvrajsingh hi. I'm back now.

yuvraj singh

Shopping in jaipur. The oldest market, johri bazar

John Rennie

@yuvrajsingh is that far from your home?

yuvraj singh

358km

From my village

But my original home is in jaipur it is around 6km

John Rennie

Wow, that's a long journey. By train?

yuvraj singh

7:40 AM

Yes I take a train night around 12 o clock.

This is India first plan city.

Deign by British architect James.

John Rennie

Jaipur was famous in the history of the Raj. Though I guess it has changed a lot since those days

yuvraj singh

Yes, but the parkota the four pillar inside which old jaipur is, same as it was during the British rule.@JohnRennie

You know sir what happened in night in train. @JohnRennie

John Rennie

@yuvrajsingh no? What happened?

yuvraj singh

Actually there was no seat available in train due to Diwali rush, so any how I got seat in sleeper class ok

John Rennie

OK

yuvraj singh

7:51 AM

So I and my brother we both are, slipping facing each other.

Suddenly a girl, I do on know is she, sat near my seat.

Ok

@JohnRennie

Hi welcome.

John Rennie

@yuvrajsingh I'm on the phone. Sorry.

yuvraj singh

Ok

John Rennie

@yuvrajsingh I'm off the phone now. It was work calling so I had to answer :-)

@Malavika hi :-)

yuvraj singh

No isaue

So she sat near by me.

John Rennie

OK

yuvraj singh

7:58 AM

But due to recent experience I am not sure to let her sit.

John Rennie

Really?

yuvraj singh

Sir I can, t describe, what kind of situation I go through these days.

user8718165

@yuvrajsingh XDXD

John Rennie

@yuvrajsingh Still a bit shaken by the incident with the robbers?

yuvraj singh

Yes.

John Rennie

8:01 AM

From my own experience it takes a while to get over things like that.

yuvraj singh

True, so I ask here where would she go.

John Rennie

There isn't a lot you can do about it except to try and take things easy until you feel better.

yuvraj singh

Yes.

user8718165

@Malavika hello...welcome to apna room ;-)

yuvraj singh

She said she will go xxxx station which is the next to next one.

John Rennie

8:02 AM

OK

yuvraj singh

So and I got to the sleep. And suddenly after some time a voice comes.

John Rennie

@yuvrajsingh yes?

user8718165

@JohnRennie thank you very much sir :-)

yuvraj singh

And what to do you think what happen next.

John Rennie

What?

yuvraj singh

8:06 AM

@JohnRennie can come in h bar once I need you.

The girl is opening the gate and was about to jump off the train.

John Rennie

@yuvrajsingh huh? While the train was still moving?

yuvraj singh

Obviously

John Rennie

Wow. So what happened?

yuvraj singh

Sir sorry but unique was total disrespecting he can, t be so rude, while writing comment. @JohnRennie

I think this is the first condition of the site to be humble. And patient. And nice to other.

John Rennie

@yuvrajsingh the moderators will be able to see the comments he posted then deleted and they will have a word with him.

yuvraj singh

8:16 AM

OK. Sir, I before I can ask the girl something her husband was there.

He start blaming me.

@JohnRennie

John Rennie

At least your brother was with you this time.

yuvraj singh

Yes.

I explain him all then that stupid girl explain she, feel vomiting, so she goes, s near the gate.

Oh good come on, my reaction.

John Rennie

Did the husband apologise to you?

yuvraj singh

No he almost beat me,

Before my brother call the railway police staff. There

John Rennie

Wow, it's been an eventful few days for you.

user8718165

8:23 AM

@yuvrajsingh It must have been a great mess:-(

yuvraj singh

What a....... It is.

@JohnRennie You like it, my holiday becomes. Like a thriller movie.

Where twist and turns are. Like. This.

John Rennie

@yuvrajsingh it'll be good to get back to college. At least there you only have physics to worry about :-)

yuvraj singh

But here family is family, after.

John Rennie

True.

yuvraj singh

So sir what is your daily diet. @JohnRennie

John Rennie

8:29 AM

@yuvrajsingh I've always liked eating really big meals, but now I'm getting older I can't eat big meals all the time or I'd get fat. So I try to eat healthy meals during the week then I eat a big meal on Saturday and Sunday.

yuvraj singh

What kind of stuff you eat generally.

John Rennie

Typically I eat rice and vegetables during the week. Very similar to a pilao made with vegetables.

yuvraj singh

Pulao right.

I do some gym so I have a definite food.

Because we eat in college mess.

John Rennie

I'm not sure how to spell it because different people spell it different ways. I think different regions of India might spell it differently. I guess it's a Hindi word so the English spelling is only approximate anyway.

yuvraj singh

Veg

Actually sir I will post my photos from tommorow onwards is it OK.

@JohnRennie

user8718165

8:34 AM

@JohnRennie sir can you share a pic of yourself?

John Rennie

@yuvrajsingh yes. It might be better to wait until after the holiday anyway so you can post them all at once.

yuvraj singh

Yes.

John Rennie

@user8718165 I don't have any recent pictures of myself ...

yuvraj singh

Please sir we want to see you. @JohnRennie

You have desktop cam.

user8718165

@JohnRennie sir you can click one please sir...delete it then :)

yuvraj singh

8:35 AM

@JohnRennie @user8718165 is right sir, delete it within a fraction of 10 second.

John Rennie

Thus is me after I got caught in the rain while I was out cycling :-)

I'm a bit wet in that photo :-)

user8718165

@JohnRennie you're looking like a real PHYSICIST from Cambridge:-)

yuvraj singh

True.

I can, t believe you are totally change, grow up some beaded it look nice to you

John Rennie

@Malavika retired now. I now work part time as a computer nerd, just to use up some of my spare time.

@yuvrajsingh the picture of me with the beard is from over twenty years ago.

I won't grow a beard again as I find it very itchy and uncomfortable.

yuvraj singh

Sir I think you should delete the photo now, so that no can misuse it. @JohnRennie

John Rennie

8:40 AM

@yuvrajsingh it's OK. I don't think the photo could be misused for anything serious :-)

Anyway it's on Facebook.

yuvraj singh

You are on Facebook, do you have some photo of your home. @JohnRennie

John Rennie

@yuvrajsingh not my house in Chester. I think there might be some photos of the village where I grew up.

yuvraj singh

Sure we are happy to see it.@JohnRennie

John Rennie

This is the sort of thing I eat during the week.

yuvraj singh

Look tasty.

John Rennie

8:45 AM

@Malavika rice and vegetables with chillies and ginger as well.

If you're on Facebook my photos are here

@Malavika my father was stationed in India during the second world war. He was there for several years and developed a love of Indian food. So we ate a lot of Indian food while I was growing up.

Though he was stationed near the border with Afghanistan so it was Punjabi food not Kerelan food.

I found a photo of the village where I grew up.

@Malavika I think rice is eaten all over India.

Is it? I've never been to the north of India.

I think biryani is popular in Pakistan, which is where my father was stationed (that was before partition).

But I know the north eat more wheat based foods.

Most of the India restaurants in the UK serve Punjabi food. Although a Kerelan restaurant has just opened in Chester. Let me see if I can find the web site.

Aha found it. Here are their menus.

I use coconut milk a lot to make meals sweeter and richer. I'm not so keen on the coconut flesh.

yuvraj singh

9:24 AM

@JohnRennie was you father a general.

Aladdin

@JohnRennie hi

John Rennie

@yuvrajsingh no, just a soldier :-)

@Aladdin hi

yuvraj singh

OK, yeh but rajasthan here. Is different from rest of India.

Do you have your office pic, I mean at Unilever. @JohnRennie

John Rennie

@yuvrajsingh no, though it might be on the web somewhere.

Unilever Research & Development Port Sunlight Laboratory

The Unilever Research & Development Port Sunlight Laboratory is the multinational consumer goods company Unilever's main research and development facility in the United Kingdom. It is located in Bebington, Merseyside. == History == Unilever's predecessor companies conducted research in Bebington from 1890 and the first dedicated research building was built in 1911 by Lever Brothers. Unilever was formed in 1929, and until 1951 Port Sunlight was its main research laboratory worldwide. === 1960s === It created a research division in 1961. In the early 1960s the site researched colloid chem...

yuvraj singh

9:45 AM

Are you going parties for. Weekend @JohnRennie

John Rennie

@yuvrajsingh I'm meeting up with some friends tonight and we're going out for a quiet drink. I'm not doing anything on Saturday or Sunday.

yuvraj singh

Aah, that, s good.

John Rennie

I used to go out a lot when I was younger, but I've got quieter as I've got older :)

yuvraj singh

Do you have batch photo while. You are in Cambridge.

John Rennie

I guess you'll be celebrating Diwali with your family.

@yuvrajsingh I have very few photos from the time I was at Cambridge.

yuvraj singh

9:50 AM

It is day after tomorrow, my all. Day went in shopping,

John Rennie

Buying stuff for Diwali? Or stuff to take back to college? Or both?

yuvraj singh

Bothfor Diwali,

Decorations here is beautiful

John Rennie

I've seen photos of Diwali celebrations and they are always really colourful.

yuvraj singh

I you will. Be amaze after watching my house.

John Rennie

@Malavika maybe I'm thinking of a different festival then?

yuvraj singh

9:54 AM

If you johri bazar Diwali you see how much traffic is here.

John Rennie

Ah, yes :-)

yuvraj singh

10:08 AM

@JohnRennie i am sharing my pic.

John Rennie

@yuvrajsingh :-)

@yuvrajsingh :-) Where did that picture come from?

yuvraj singh

near the railway track i clicked it yesterday .@JohnRennie

John Rennie

@yuvrajsingh you must have linked the wrong picture ...

yuvraj singh

no it is me @JohnRennie

John Rennie

That's what you linked ...

yuvraj singh

10:14 AM

yaa its my pic @JohnRennie

John Rennie

OK :-)

yuvraj singh

kidding sorry he is my brother @JohnRennie

by mistake

are you there sir.

John Rennie

:-)

yuvraj singh

i think you are busy.

what you think

do you have your pic .@Malavika

come on you can delete it after upolading it.

@JohnRennie can you delete both the pics please sir.@JohnRennie

i think upload the correct one.

i also request @user8718165 @Malavika how they look like,

John Rennie

Deleted

@yuvrajsingh Done! :-)

yuvraj singh

10:49 AM

No

yuvraj singh

12:05 PM

Bro that stupid continously targeting me @JohnRennie @user8718165

user8718165

@Malavika I thought we could make a group and chat together there...:-)

@yuvrajsingh are you talking about user unique?

yuvraj singh

I down vote because answer deserve the down vote, instead of Improving he is giving moderator stupid comments.

Yes @user8718165

user8718165

@yuvrajsingh bro don't get freaked out and reply to him... Let him spam...a mod will definitely see that...let it be ACM mod...he can teach a lesson :-)

yuvraj singh

Actually I saw his some post, where answer either answer need improvement or it is wrong so what was wrong in it

user8718165

@Malavika that's fine...no worries ;)

yuvraj singh

12:14 PM

And he tried for a permanent ban over me. @JohnRennie @user8718165

user8718165

@yuvrajsingh leave him....it's Diwali time....don't waste your time with that guy....enjoy

@yuvrajsingh he can't do that.... The mods will always be fair....

yuvraj singh

Correct, but if the moderator point out me unnecessary like will leave the site.