Problem Solving Strategies

John Rennie

05:27

f anyone is interested, there are copies of the university of Oxford entrance exam here.

2

Nehal Samee

06:40

@JohnRennie nice ...

Anonymous

They are on average simpler than JEE advanced, but subjective.

Nehal Samee

Yes. No hardcore chemical reactions.

Anonymous

I didn't see the chemistry papers.

Anonymous

What are they called? CAT, like PAT for physics?

Nehal Samee

Oops ... There were separate chemistry papers !

@IceInkberry I think so.

Anonymous

06:52

What is anonymous? Does that mean deleted account?

John Rennie

@IceInkberry I got impression JEE is a bit harder. The material covered is roughly the same, but the JEE questions are a bit trickier.

Nehal Samee

It seems like it was blue ..

Anonymous

@JohnRennie True. Tricky maybe the right word.

user253190

@IceInkberry Yes, a result of me deleting the Physics SE profile

Anonymous

Its level is like between JEE(mains) and JEE(advanced), more oriented towards advanced.

Anonymous

06:58

@Blue Ooh. That happens when you delete profile

user253190

I'm restricting my activity to the QC SE site for now

user253190

@IceInkberry Yeah

Anonymous

Oh, great. (But, that shouldn't happen since chat is linked to our common SE profiles? Silly doubt.)

user253190

@IceInkberry Yeah, but I had requested for deletion of the chat profile too

Nehal Samee

@JohnRennie basically , we shall add up the currents ... Then for middle one , shall we take 2/3 or 4/3 ... ?

John Rennie

07:11

@NehalSamee for each resistor you add up the currents through that resistor to get the total current. Then the voltage drop across the resistor is given by $V = IR$.

In the middle diagram the total current flowing out of the battery is 4/3A but the current flowing through any one resistor is 2/3A.

Nehal Samee

07:24

@JohnRennie ... If I'm said to find the total current of the circuit ... which numbers should I add ?

John Rennie

@NehalSamee I'm not sure how you'd define the total current ...

Nehal Samee

@JohnRennie ummm .. then the legitimate question would be to find voltage drop across each resistor ?

John Rennie

Yes. Jasmine didn't say exactly what was being asked but my guess is that you'd be asked to find the voltages at all the nodes.

Nehal Samee

@JohnRennie for three diagrams , I add three currents ( if there are ) through a specific resistor to find voltage drop ?

John Rennie

Yes

Nehal Samee

07:27

@JohnRennie thanks...Done

John Rennie

I think people have said that superposition isn't taught at JEE level, but it's a very useful technique to know.

And it's very simple to use.

Avnish Kabaj

07:38

@JohnRennie that technique is good sent

Makes life so easy

*god

samjoe

i was going to buy asus zenfone max today, sale was on 12 noon, sold out within seconds

meh

Jasmine

samjoe

@Jasmine best to use parallel combination of batteries in such questions

Avnish Kabaj

@Jasmine this is from the fiitjee package

Use superposition

Jasmine

@JohnRennie I solved it by kirchhoffs law but got little confused using superposition

Avnish Kabaj

07:46

Literally in 30 sec

Jasmine

@AvnishKabaj yeah

Avnish Kabaj

It's very simple

Jasmine

@samjoe what's that

Avnish Kabaj

Remove all the batteries

Other than one

samjoe

Nah nah nah nah its very easy with parallel comb of batteries

Jasmine

07:47

@AvnishKabaj I got different answer

samjoe

I mean easier

Avnish Kabaj

Yeah this one is easier

John Rennie

@Jasmine are those the internal resistances of the batteries written alongside the voltage?

Avnish Kabaj

Using parallel

Direct formula

Jasmine

@JohnRennie yes

samjoe

07:48

What do we have to find @Jas

Jasmine

Current in all branches

John Rennie

@Jasmine when you have a battery with an internal resistance you do superposition by removing te battery but leaving the internal resistance there i.e. you replace the battery by a resistor equal to the internal resistance.

Jasmine

@JohnRennie oh you mean that I should suppress internal resistance of others

John Rennie

@Jasmine No, a battery with an internal resistance is equivalent to an ideal battery and a resistor in series.

You remove the batteries but leave the internal resistor there.

I can draw a diagram if you want.

Jasmine

@JohnRennie that's why I guess I didn't get the answer

samjoe

07:52

5/13 current on left, just check please

Jasmine

@samjoe correct

samjoe

yeah B-|

Jasmine

samjoe

Actually its a method to convert parallel combination of batteries into a single branch

Jasmine

@JohnRennie is this is one part of the 4 diagrams correct?

samjoe

07:57

Three branch, combine two so we get two branches, now finding current is easy. Again do this for second branch.

Jasmine

I know only when + terminal connected to - then we add

John Rennie

@Jasmine yes

Jasmine

@JohnRennie hmm I got

@samjoe can you explain more I don't get

How do I use battery combination

John Rennie

Jasmine

08:12

@JohnRennie I could do by superposition but samjoe could tell the answer quickly bunt battery combination so I was asking that

I want to know how to apply combination of batteries.

@JohnRennie what do you use to draw such amazing diagrams?

John Rennie

I'd guess Sam means this ...

@Jasmine I use Google Draw. But that only really works well on a PC. If you're using a phone it's hard to draw good diagrams.

Jasmine

@JohnRennie that confuses me as I knew that when - and - are on the same side we substract but that is also true for + I didn't know but yeah if - and - face towards each other if we see from other side then the positive terminals are also facing towards

@JohnRennie this is awesome if now I apply superposition this is way more easier than kirchhoffs law

John Rennie

@Jasmine start at the top left corner and move vertically down to the bottom left corner. The first battery adds +2V then the second battery adds -1V, so together they give +1V.

If you're ever in doubt how to combine batteries just imagine a path through all the batteries you want to combine and add up all the voltages as you pass through them.

Jasmine

@JohnRennie hmm

I really feel that superposition should be taught it makes live very easy

John Rennie

08:33

@Jasmine I'm surprised it isn't taught, especialy since it's so easy to use.

samjoe

No @John I meant combining different branches, two into one branch. There is a formula for that

John Rennie

@samjoe Ah, OK ...

samjoe

In your image, we can combine the right and central branch to get a single branch, so that we can find current in left branch

Sid

@JohnRennie Superposition can be slightly confusing in Ideal Parallel circuits

samjoe

while the superposition method would be more general i guess

John Rennie

08:42

Shrug. No single tool is perfect for every situation.

Sid

Point taken

samjoe

More general than battery combination i mean

@Jasmine Suppose you need current in only left branch. Then the central and right branch can be combined, giving a $E_{eq}$ and a $R_{eq}$. Subscripts $1,2$ denote the corresponding qty of branches being combined. then $E_{eq} = (\sum\frac{E_i}{R_i}) R_{eq}$ and $\frac{1}{R_{eq}}= \sum(\frac{1}{R_i})$

Avnish Kabaj

08:59

Cotton eyed joe

Anonymous

14:22

Anonymous

Is there any way I could find the equivalent capacitance without nodal analysis here?

Nehal Samee

14:33

You can apply symmetry

user187604

@samjoe hi...

@NehalSamee does vertical symmetry work here?

Nehal Samee

@user187604 ...I prefer to take symmetry line slantly passing through A or B ...

samjoe

15:01

@user187604 hi!

Jasmine

@samjoe today only we were taught grouping of cells. Now i see how it works

@JohnRennie true today only i got problems in which superposition confused me

My teacher always use nodal point to solve the question and i am just confused

samjoe

What confuses you, nodal method is actually very straightforward. It's about marking potentials and using q=CV or v=iR

@IceInkberry think in terms of 3D cube, ;)

Anonymous

@samjoe Actually, the thing is, I converted 3D cube to that structure :P

Jasmine

Network Theory - Nodal and Mesh Analysis | GATE Preparation Lectures | EC, EE, IN

►

samjoe

Lol you should then diagonally squish it

Anonymous

15:12

That means, my question is that how do I do that without nodal analysis?

Jasmine

@samjoe this man confuses me

Anonymous

@samjoe Didn't get

samjoe

Instead of smashing it's face

@IceInkberry I'll add an image

Jasmine

Why does he assume that that the node he take has highest potential

Our teacher told nothing like that

user187604

@samjoe hello man

Anonymous

15:18

Superposition is awesome.

Anonymous

Quick and easy solution to problems - Superposition!

samjoe

Sid

@IceInkberry Not for parallel circuits though. Still, it's one of the best methods to solve circuits

samjoe

@IceInkberry lol I was reading your story

@user187604 do you plan to go anywhere beyond this customary greeting? :)

Sid

@samjoe You can, in edit history. :P

user187604

15:21

@Sid @samjoe I wanna get a distance learning course. Which should be better?

samjoe

@Sid I'm such a noob. Didn't know that، is that power only for owners

Sid

@samjoe Nope. Everyone.

user187604

@samjoe yep obviously :p

samjoe

I'm on phone @Sid

Sid

Room Owners only have power to kick people out of rooms and to move messages to different rooms.

(If you unnecessarily kick people, then you get suspended. So, wield power with responsibility)

user187604

15:23

1 min ago, by user187604

@Sid @samjoe I wanna get a distance learning course. Which should be better?

Sid

@user187604 DIstance Learning Course, for what?

samjoe

He's dropping

user187604

@Sid for kvpy Sb and jee advanced 2019.

@samjoe please see ^^^

Jasmine

samjoe

@user187604 you can't give kvpy on drop year.. I mean you can take the test but you won't be selected .. so what's the point

Jasmine

15:25

How do i solve it

samjoe

@Jasmine with nodal you'll need 2 variables probably

Jasmine

While taking nodes we must take the direction of flow of current in accordance of higher and lower potentials right?

samjoe

@ice sorry forgot to tag, is the image fine

user187604

@samjoe my parents say me to not to drop just get an admission and try these next year..... So I am getting a college. I don't think vector calculus learning and mechanics would be so hard to learn in first year. So to keep me in a pressure I need a course...

Anonymous

Ahhhhh, my net is so slow that I can't even load images and can't go to edit history(which I was actually doing). But now, I do not dare to refresh. Thanks to my Internet.

samjoe

15:28

@IceInkberry is it MTNL

user187604

Airtel?

1 min ago, by user187604

@samjoe my parents say me to not to drop just get an admission and try these next year..... So I am getting a college. I don't think vector calculus learning and mechanics would be so hard to learn in first year. So to keep me in a pressure I need a course...

Jasmine

@samjoe in your pic between X and y there will be capacitor probably

samjoe

@user187604 maybe then you can give kvpy, but you need to check, I guess only those who are in pure sciences can give kvpy in college, but do check..

Anonymous

@samjoe Jio, Airtel nothing is working since the start of rains.

samjoe

@Jasmine I Thot noone will notice :)

user187604

15:30

@samjoe I wanna go for physics honors man...

Anonymous

So, I'll see the image later.

Jasmine

@samjoe sorry it was just an not necessary point out

user187604

So which distance course should I take? @samjoe @Sid

Jasmine

@samjoethe question i posted cant be solved by superposition as stull cant figure out whats in parallel and whats in series

samjoe

@user187604 oh yea so then you'll be alright. For jee I think you can enroll in a regular test series, say that of allen, or resonance or fiitjee etc. For study material idk what to say

user187604

15:33

@samjoe I mean should I take fiitjee distance course or Allen or anything else?

Anonymous

I thought you spelled Allen as Alien :)

user187604

@IceInkberry I also spelt resonance as response :p

samjoe

@Jasmine are cool nvm. For your question, you can't use series parallel simplification.. since you have taken right point as zero volts, say centre top point is x volts and left centre point as y volts

Sid

@IceInkberry You can, if you write the i in block letters.

Anonymous

@Sid Puzzle people think like that :P

samjoe

15:35

@Sid and using sans serif :p

@IceInkberry agreed cent per cent

Jasmine

@samjoe in my question we cant use superposition then?

user187604

2 mins ago, by user187604

@samjoe I mean should I take fiitjee distance course or Allen or anything else?

samjoe

I guess you can, haven't tried but you can I think..

Sid

@IceInkberry Oh, you have no idea what else we think. Like, "Nod" means No d. "indeed" means "in deed"(That is, insert something within the word "deed")

Jasmine

@samjoe but it does no help

@Sid over the horizon thinking

Sid

15:38

and EE means English Etymology. :P

user187604

@Sid chat.stackexchange.com/transcript/message/45032749#45032749

samjoe

@user187604 dude I don't know about that, any one will be decent.

user187604

Got it

Nehal Samee

@Jasmine do you have to find equivalent resistance ?

samjoe

@user187604 do some research, as in consult some friends who have taken either of the material.. apart from that do focus on ncert, hcv, etc std books

Jasmine

15:43

@NehalSamee current is required in each branch but yeah if i do it by superposition i need to find equivalent resistance which is still hard to find

@NehalSamee you can do it by kirchhoff's laws but i was thinking of nodal method and superposition

samjoe

@Jasmine yeah with superposition you'll need star delta conversion

Jasmine

@samjoe now whats that!!!!!!!!!!!!!!!!

I have heard the name from you people only

samjoe

It's just a formula

V. Famous

Jasmine

Whats the formula

samjoe

Must be on Google or somewhere

Jasmine

15:50

Star to Delta Conversion (With Proof and Example)

►

This ?

samjoe

Yeah but you'll need reverse conversion here

Jasmine

Means delta to star?

Nehal Samee

Right ... Ahh. . I forgot that ...

There is Delta to star formula too ...

Jasmine

Really seems like i need to learn a lot

Nehal Samee

There is Y to Delta too ..

Jasmine

15:55

Do you mean these formulae?

@samjoe ^

Please confirm

samjoe

16:10

@jas yeah

But why not try nodal also, it's two equation two unknown

Jasmine

16:21

@samjoe yeah i finally got through nodal my x=-10 and y=0

user187604

@samjoe thanks man.

Feeds

16:40

Mithrandir24601 has added Blue to the list of this room's owners.

Sid

@Feeds Wasn't Blue already a roomowner?

Mithrandir24601

17:11

@Sid Yes (or at least, that's what I'm told), but there have been a couple of issues today with @Blue's chat profile

Anonymous

17:21

@Sid Yes, but I had earlier (around 2 months back) requested for the deletion of my Physics SE profile along with the associated chat. That (the chat profile deletion) took place today morning, which resulted in me being removed from the RO position.

Sid

Oh. Okay.

Anonymous

@Sid Oh, I know. When you overthink stuff and the answer is something really easy "Whuttt suchhh questioooon"

Sid

@IceInkberry that's a very common phenomenon known as "Student Blindness", characterized by words like "duh" when the students see the answer.

Anonymous

@Sid That's something new

Anonymous

Will steal that term :)

Anonymous

17:36

Actually, I do think there's a word for it

Sid

@Blue That term isn't mine. It's half-plagiarized from "defender blindness" which we use in Contact. :p

Anonymous

Which I obviously can't remember at the moment

Anonymous

@Sid What's that Contact thing you Puzzling SE guys keep playing?

Anonymous

Some word guessing vocab-based game I suppose?

Sid

@Blue Basically contact is, 'Guess the word that the defender is thinking". Someone volunteers to be a defender. They then give the first letter of the word that they have thought. The other players "attack" the defender by giving clues about certain words(either by simple def or wordplay) which the defender has to guess.

If say, Attacker 2 correctly deduces what word Attacker 1 was cluing, they say "contact [Clue number]". If the defender can't guess the word, they "pass" and Attacker 2 then answers. If the answer is correct, Defender has to give up another letter of the word.

And so on the game continues till someone finds out what word the defender was thinking or if the defender has exhausted all the letters of the word.

Anonymous

17:44

@Sid What if the defender changes the word they're thinking of, midway?

Sid

@Blue They can't. (Of course, it's impossible to know if they did. But, we expect people to be decent and honorable)

Anonymous

@Sid BiG AsSuMpTiON ;)

Anonymous

Well, it does sound interesting :)

Anonymous

When is it held normally? Every week?

Sid

(To be honest, if they did, they are wasting their own time too. So, it's not really in their interests to change their word midway)

@Blue Depends when people are free and if enough people are around

Anonymous

17:47

@Sid Oh, I thought it was some set weekly event. Gotcha.

Sid

(it used to be a weekly thing. But then, people got busy and no one had time for a full-fledged game)

Anonymous

Makes sense

Transcript for

Problem Solving Strategies