Problem Solving Strategies

Harshavardhan Hajeri

02:23

@satan29, do you have cengage pdf? if so, can you help me find it

Also, if anybody has pdf for mathematics mcq by a das gupta, bharati bhavan publishers, please share... thank you

satan 29

04:56

@HarshavardhanHajeri hi!

unfortunately no, i have its hard copy.

Priya

05:59

Hi all! i need a small help in the a question in rotational mechanics:

Here there are 3 particles attached to a ring and the ring is rolling without slipping

we are asked to find the kinetic energy of the system

satan 29

@Priya hi!

Priya

when i calculated KE using iaor,

satan 29

yes, thats exactly what i was about to do

Priya

@satan29 hi!!

i got 6mv^2

and it's also right as per the book

but when i did it by assuming this as a combination of translation and rotation, i got 5mv^2. so why does the second method fail?

this is how i did:

translational KE=1/2 5mv^2

rotational KE= 1/2 (5mR^2).(v^2/R^2)=1/2 5mv^2

adding both we get: 5mv^2

why is it short by mv^2 from the correct answer?

@John Rennie sir. Hi! Can you please clarify my query if you are free ?

John Rennie

@Priya I'm answering a question in another room. I'll ping you when I'm free.

satan 29

06:12

@Priya what did you get for I_{com} of the system?

Priya

ok sir. thank you!

@satan29 5m R^2?

satan 29

i think the issue is that

Priya

all the masses are distributed in the periphery, so the new ring mass can be assumed to be 5m.

satan 29

the COM isnt the geometric center

Priya

ah. yes. thanks. I think that's the reason for the anamoly.

@John Rennie sir, i think @satan 29 cleared that doubt. sorry for the disturbance. i dont think there's any other reason. thanks.

ronak jain

08:43

@satan29 Hi

satan 29

hi

ronak jain

@satan29 actually I wanted to know that which app should I use to draw images to explain question as John rannie is using ?

satan 29

google draw

ronak jain

@satan29 do you know about any such ?

satan 29

thats what he uses

ronak jain

08:50

Ok thanks

Can you tell me a think about single slit diffraction

satan 29

i am afraid diffraction is not something i know a lot about

ronak jain

Ok

If you want to just know the problem and try that....

Please ping me

@satan29 do you not even want to try ?

Abram Ivanov

10:01

@JohnRennie sir do you remember this question?

i am having problem in it's acceleration

the mass m on left has acc g

right one has 3g

as stated in my book, i don't know how or why

@JohnRennie are you busy sir, lemme know i can come back later

John Rennie

10:17

@AbramIvanov hi

Abram Ivanov

hi sir

i wont take much time

John Rennie

@AbramIvanov and the pulleys are massless?

@AbramIvanov hello ?

Abram Ivanov

@JohnRennie sorry sir

i am back'

@JohnRennie yes

John Rennie

Abram Ivanov

i dont understand the motions

aren't they complex?

John Rennie

10:24

This is my problem with the question. Look at the distances a and b I have marked on the diagram. The length of the string is L = 2a + 3b plus this bits wrapped round the pulleys, but these are constant so I'm going to ignore them.

Abram Ivanov

@JohnRennie no problem till here

John Rennie

Now suppose the left pulley moves down some distance x. Then the distance a increases to a+x and the distance b decreases to b-x

So the length of the string changes to L = 2(a+x) + 3(b-x) = 2a + 3b - x

i.e. if the left pulley moves down then the length of the string decreases, and physically this means the string would go slack.

Abram Ivanov

@JohnRennie wouldn't the right pulley move too? so we should take it's effects in measure

John Rennie

All I'm doing here is asking what happens if the left pulley were to move down ...

Abram Ivanov

ok

John Rennie

10:28

The point is that the left pulley is massless so it can move in response to the slightest force, and we've established that if it moves up the string goes slack.

Abram Ivanov

@JohnRennie is it possible to have such a scenerio in real?

@JohnRennie now it's much clear

John Rennie

That means the tension in the string must be zero, because if the tension was non-zero there would be a force on the left pulley and it would instantly move.

Abram Ivanov

@JohnRennie yes now that's easy to imagine

John Rennie

@AbramIvanov well, real pulleys aren't massless.

Abram Ivanov

if we take like really light pulleys

plastic ones maybe

John Rennie

10:31

As soon as you give the pulleys a mass the problem becomes much harder because then the pulleys will have a non-zero moment of inertia so they have a rotational kinetic energy and rotational acceleration.

The point is that I don't see how the question can be asnwered as it is.

Abram Ivanov

ok

@JohnRennie thanks!

John Rennie

@AbramIvanov Do you want to post the whole question so I can see exactly what it asks?

Abram Ivanov

11:27

@JohnRennie just down this is the image, and i was aasked to find tension in strings and acc of blocks

assuming pulleys and strings are ideal

ronak jain

12:05

@HrishabhNayal hi :-)

Hrishabh Nayal

@ronakjain Hey

ronak jain

@HrishabhNayal do you know all about single slit diffraction ? Actually I was having a print in that

Hrishabh Nayal

@ronakjain I do not know all about SSD.

@ronakjain Print?

ronak jain

@HrishabhNayal Wait....actually John Rannie told me the fringes of single slit as in the following figure....I am going to Post....

@HrishabhNayal did you get it ?

Hrishabh Nayal

@ronakjain yes

ronak jain

12:09

@HrishabhNayal he said that the fringe height is only upto the slit. It means that it is extended to X = -infinite to + infinite

But it's height is just unit length

Now the problem comes.....

@HrishabhNayal as i know YDSE is also a double slit diffraction similar to this .....

But light there enters from two slits.

Now have a look at this image .....

@HrishabhNayal are you agree with me till now ?

@HrishabhNayal are you gone somewhere ? Say atleast yes or no

Hrishabh Nayal

@ronakjain I am having difficulty following you but go on

@ronakjain Lets say I agree

ronak jain

@HrishabhNayal what you haven't understood yet ?

Don't agree until you are really not satisfied. Just tell me where you did not understand ?

Hrishabh Nayal

@ronakjain Go on ask what you feel is contradicting

ronak jain

So if the pattern of the fringes is in just front of the slits than as I think that they are not having any overlapping area. Is it right ?

Hrishabh Nayal

@ronakjain Why do you think fringes are only at front?

ronak jain

12:15

So if they are not overlapping so I think that in YDSE we should get two different fringe patterns

Yes

John rannie had explained that they are in just front of the slit extending from X = - infinite to + infinite. And they are not extended along the y axis

@HrishabhNayal what do you think about this ?

Hrishabh Nayal

1

A: How can a bright fringe be not as bright as a dark fringe in YDSE?

If you have a single slit it will produce a diffraction pattern where there will be maxima and minima in intensity. So the light from a single slit has "preferred" directions of travel. Another single slit close to the first one will also produces a diffraction pattern. If the two single sl...

The answer has a image look at it

ronak jain

Wait....let me check

@HrishabhNayal yes I have also gone through such image

Hrishabh Nayal

en.m.wikipedia.org/wiki/Double-slit_experiment. See the image in overview

ronak jain

But have a look at the fringe pattern of single slit

I know all these

But did you look at the image of single slit diffraction

Hrishabh Nayal

@ronakjain what about it?

ronak jain

12:20

@HrishabhNayal if you have looked at the image I posted than you will find that the fringes height is just equal to the length of slit. That is L = 1

Hrishabh Nayal

@ronakjain seems right

ronak jain

@HrishabhNayal so if the two slits are seperated by some distance than I hope that the fringe pattern of each slit will also be separated.

Hrishabh Nayal

@ronakjain Oh I think I get it . What orientation do you think slits are in? Horizontal or vertical?

ronak jain

@HrishabhNayal just look at the image. I am assuming the slits to be vertical and it's width to be very small

@HrishabhNayal so did you understand my problem ?

Hrishabh Nayal

@ronakjain well the pattern then extends on X axis right?

ronak jain

12:25

@HrishabhNayal yes it extends in X axis

Hrishabh Nayal

@ronakjain So if double slits are vertical the pattern that each of them produces will extend along X axis?

ronak jain

@HrishabhNayal yes

Hrishabh Nayal

@ronakjain And that is where the pattern "intersects"

Can you see now?

ronak jain

@HrishabhNayal yes that is the real problem I am facing ?

What do you want to show ?

Hrishabh Nayal

@ronakjain I dont think I still get your problem

If the slits are vertical they interfere along X axis

ronak jain

12:28

@HrishabhNayal are you agree that the pattern of each slit will not be interesting ?

Hrishabh Nayal

@ronakjain Intresting?

ronak jain

No intersecting .

Are you agree ?

Hrishabh Nayal

@ronakjain Hey I have to run an errand. Will be back in about 5 min

ronak jain

@HrishabhNayal are you agree ? Yes or no

Ok

@HrishabhNayal ping me when you are back

Hrishabh Nayal

@ronakjain hi

ronak jain

12:37

@HrishabhNayal are you back ?

Hrishabh Nayal

Yep

ronak jain

@HrishabhNayal so did you get my problem now

Hrishabh Nayal

@ronakjain they should sort of "overlap"

Heisenberg's Uncertainty Principle Explained

►

See this , particularly the setup

Ignore the HUP talk

ronak jain

Hey ! Are you saying that I have made the wrong setup for the slits

Hrishabh Nayal

@ronakjain I think you are messing up vertical and horizontal

ronak jain

12:39

Do you think that the setup should be like....I am posting here

Hrishabh Nayal

Just a vague guess but ... worth a shot

@ronakjain Ok

ronak jain

Yes in this situation they will overlap

Hrishabh Nayal

@ronakjain yes

ronak jain

And in my setup will we get two fringe patterns ?

Hrishabh Nayal

@ronakjain This one?

ronak jain

12:41

@HrishabhNayal no old one

Hrishabh Nayal

@ronakjain When fringes are horizontal?

ronak jain

@HrishabhNayal yes

Hrishabh Nayal

Well then you get pattern along Y axis

ronak jain

In this

Won't we get two fringe patterns ? They don't look to overlap

Hrishabh Nayal

You get it?

ronak jain

12:44

Tell me that won't we end up with two different fringe patterns in the above arrangement ?

Hrishabh Nayal

@ronakjain Consider this setup but with one slit

ronak jain

Yes

Hrishabh Nayal

What do you expect to see?

ronak jain

Fringe patterns along the x axis

Hrishabh Nayal

@ronakjain And where do you think patterns lie in this diagram?

ronak jain

12:47

In the diagram I had firstly shown. The two screens I have shown . There will be the fringe patterns

Hrishabh Nayal

@ronakjain yes but along?

ronak jain

X axis

Hrishabh Nayal

Both of them right?

ronak jain

Yes

Hrishabh Nayal

So they overlap?

ronak jain

12:49

No . They are both parallel to x axis and separated by some distance

They are just two lines parallel to x axis like y = 1 and y = 2

Did you get it ?

Hrishabh Nayal

@ronakjain Are they?

ronak jain

@HrishabhNayal yes they are just like two lines parallel to x axis

So they won't intersect

Are you agree now ?

Hrishabh Nayal

@ronakjain Try rotating this by 90 degrees

Is it now equivalent to your setup?

ronak jain

Which setup ?

I have posted two setups

If in this setup you rotate the slits by 90....

Hrishabh Nayal

@ronakjain Yes this one rotate by 90 you get other setup

ronak jain

12:54

Yes

But I don't think that in that case we will get any diffraction pattern because than the slit width will be finite

Hrishabh Nayal

@ronakjain So do u see it now?

ronak jain

Yes

I am asking of the situation when one of the slit is replaced from this position to below the other slit without changing orientation

Hrishabh Nayal

@ronakjain Ah I see. Then you get 2 diffraction patterns

Non overlapping

ronak jain

Yes...that was I going to say

Just bring the other slit below the second one

And you will get two diffraction fringes

Hrishabh Nayal

So what is confusing there?

ronak jain

12:58

Yes I have also cleared now.

Actually I was firstly considering the arrangement in which there are two patterns ....and thought that if there is not any interference than what is YDSE saying about ?

@HrishabhNayal ok

Hrishabh Nayal

@ronakjain So you were confusing where the slits are placed?

ronak jain

@HrishabhNayal just leave it . I have other problem also

Hrishabh Nayal

@ronakjain As you say :-)

ronak jain

@HrishabhNayal have you also read in books that each point on slit act as a source of secondary wavelets

Hrishabh Nayal

@ronakjain In diffraction? yes

ronak jain

13:01

Yes

Wait a minute...

Have you heard that each point on slit acts as a source of secondary wavelets

Hrishabh Nayal

@ronakjain Yup

ronak jain

And these are spherical

@HrishabhNayal so why the height of fringe is not above and below L ( the length of slit )

Hrishabh Nayal

@ronakjain Are you talking about Huygen's wavefronts?

ronak jain

Yes

In NCERT also they use the same thing.

They say that each point on it acts as a source of secondary wavelets

Hrishabh Nayal

I might have to think about what limits the height. Gimme a minute

ronak jain

13:06

@HrishabhNayal ok

@HrishabhNayal according to John rannie the light gets diffracted only along the horizontal not in the vertical direction

Hrishabh Nayal

@ronakjain Hmm maybe the waves above get cancel out or maybe it has something to do with infinitely thin slit? But those are just wild guesses

ronak jain

No

That is not possible . Because if that would be....

Hrishabh Nayal

@ronakjain I am reading Wikipedia on diffraction lets see if I get something

ronak jain

Than the intensity along the vertical would be varying . But John Rannie said that the intensity along the vertical is constant

Hrishabh Nayal

@ronakjain en.wikipedia.org/wiki/Diffraction#/media/…

ronak jain

13:12

@HrishabhNayal let me see

Hrishabh Nayal

See the image

See how they null

ronak jain

@HrishabhNayal sorry, but I didn't find anything useful in that

@HrishabhNayal and also John rannie had said that they are not diffracted along vertical direction

And if you say that they cancel out....

Hrishabh Nayal

@ronakjain Does that mean waves do not travel vertically?

ronak jain

Than why the intensity along the vertical is constant everywhere

Yes, after passing through the slit they don't get diffracted along vertical

Hrishabh Nayal

@ronakjain Didn't you ask why?

ronak jain

13:16

I am not quite sure about it. So wanted to discuss it with John rannie . But he left Stack chat

@HrishabhNayal have you any idea about it ?

Hrishabh Nayal

@ronakjain Let me see what I can come up with

ronak jain

Ok

Hrishabh Nayal

@ronakjain I might get nothing at all though

ronak jain

@HrishabhNayal do you know anyone who can help me ?

Hrishabh Nayal

@ronakjain Why don't you ask on main site? Seems like a conceptual question

ronak jain

13:19

@HrishabhNayal do you know anyone like John rannie sir who has a great knowledge like him ?

@HrishabhNayal but that will be time consuming

Hrishabh Nayal

@ronakjain Could still be faster than me

ronak jain

@HrishabhNayal but if that's the last option than I would like to wait till tomorrow for John rannie sir

@HrishabhNayal do you know about persons like John rannie sir ~

Hrishabh Nayal

@ronakjain I heard ACuriousMind is knowledgeable

ronak jain

@HrishabhNayal yes

Hrishabh Nayal

Generally at h bar

ronak jain

13:21

@HrishabhNayal who is he ? Is he bhavay

Hrishabh Nayal

The h Bar

General chat for Physics SE (physics.stackexchange.com). For M...

5

ronak jain

@HrishabhNayal are you also preparing for jee ~

Hrishabh Nayal

@ronakjain Yes! how bout you?

ronak jain

@HrishabhNayal I also

Hrishabh Nayal

@ronakjain If you wanna share your Jan score? Mine is 97

ronak jain

13:23

@HrishabhNayal do you face problems in inorganic chemistry ?

That's really low 94.6

@HrishabhNayal that's nice

Hrishabh Nayal

@ronakjain Innumerable :-(

ronak jain

@HrishabhNayal why ?

@HrishabhNayal are you from any coaching ?

@HrishabhNayal are you gone somewhere ?

Hrishabh Nayal

@ronakjain Sorry power cut

@ronakjain No

@ronakjain Memory issues maybe?

ronak jain

@HrishabhNayal than I think you really worked hard for that result ?

@HrishabhNayal where do you get your doubt resolved ?

Hrishabh Nayal

@ronakjain I like to think otherwise

ronak jain

13:28

@HrishabhNayal do you face problems in inorganic chemistry ?

Hrishabh Nayal

@ronakjain I try to work them out myself mostly and sometimes Chemistry.SE

@ronakjain Isn't that what you just asked?

ronak jain

@HrishabhNayal can you give me some tips for that. I really hate inorganic chemistry

Hrishabh Nayal

@ronakjain why haven't u asked your doubt at hbar yet?

ronak jain

@HrishabhNayal I think they are discussing on a different problem and they might not look at my problem now ?

Hrishabh Nayal

@ronakjain I usually just mug everything up in hopes that I will not have to face chemistry in Engineering

@ronakjain ok

ronak jain

13:30

Ok

@HrishabhNayal which books do you follow for you preparation ?

Hrishabh Nayal

Not very helpful i know

@ronakjain Only NCERT for inorganic

ronak jain

@HrishabhNayal so how do you prepare ?

Hrishabh Nayal

N.Avasthi for Physical

ronak jain

Is ncert sufficient for inorganic ?

Hrishabh Nayal

@ronakjain I feel so

Himashu Pandey for Organic

ronak jain

13:34

What about physics ?

Hrishabh Nayal

@ronakjain I did HCV during 11th and then I left it in 12th

I moved to D C Pandey in 12 th

I never completed any of the though

Mainly cause I am Lazy

ronak jain

Oh ....

Hrishabh Nayal

And now I regret it

So I am currently just doing as many problems as I can

Wherever I can find them

Same goes for maths

ronak jain

@HrishabhNayal do you have any physics problem to share ?

Hrishabh Nayal

@ronakjain What do you mean?

ronak jain

13:40

Just any problem which can strengthen my topics also in physics.

If you find so problem that might be useful for jee

Hrishabh Nayal

@ronakjain Try NTA's mock tests maybe?

ronak jain

I have also my books to solve and test series. So I can't give time to them . If you find any such conceptual problem than share with me

Hrishabh Nayal

@ronakjain I occasionally share problems I do not understand here. Maybe you can look at them?

ronak jain

Ok

ronak jain

14:02

@HrishabhNayal you said about ' A curious mind ' but he is not showing any interest to answer

Hrishabh Nayal

@ronakjain I never said he'd answer. Just he is knowledgeable.

ronak jain

Yes. I was just telling you

Hrishabh Nayal

@ronakjain Try main site. That should be your best bet right now

The h Bar

Transcript for

Problem Solving Strategies