Problem Solving Strategies

Sakazuki Akainu

12:45 AM

@MadhuchhandaMandal i cleared JEE last year; i was just here to see what's this area, never been here before

this area seems fun :P would've loved it had i found this back then!

Madhuchhanda Mandal

7:02 AM

Anyone there?

Yashas

7:29 AM

!

@DiyankoBhowmik Physics part 2 was 3x lengthy

@DiyankoBhowmik Biology was 0.33x lengthy? :P

Biology students had an advantage this time

@SakazukiAkainu It wasn't there back then

@OsheenSachdev It was out a week ago lol

Anonymous

8:03 AM

@Yashas I have a question about reflection of light from thin films. Are you interested?

Yashas

yes

Anonymous

4. Physics | Wave Optics | Colour of a flower pot | by Ashish Arora

►

Anonymous

Okay, so in this video

Yashas

I have slow net until 8th :/

32kbps

can u write it down?

Anonymous

Okay, I'm summarizing it

Anonymous

8:05 AM

There is a thin film on a metal plate

Anonymous

The film is transparent

Anonymous

And has thickness 3000 A

Anonymous

And refractive index 1.5

Anonymous

Now, what will be the path difference between the light rays ?

Anonymous

Which are reflected from either of the surfaces of the film

Yashas

8:06 AM

$2d n sin \theta$?

+ pi

ok I screwd it up

+ lambda

not pi

Anonymous

There will be +lambda at both the surfaces, right?

Yashas

wait

two reflected?

from either side?

Anonymous

The metal is more optically dense than film

Anonymous

I'm uploading a picture

Yashas

I did not understand "Which are reflected from either of the surfaces of the film"

Anonymous

8:07 AM

wait a sec

Yashas

the thin film is on top of the metal

when you said reflected, I took one as refracted and other one as reflected

the refracted one is the one which got reflected inside

Anonymous

Anonymous

Can you see the picture?

Anonymous

Over here, they added lambda/2 only for the upper surface

Anonymous

But not for the lower surface

Anonymous

8:09 AM

Why is it so?

Anonymous

I think the path difference should be just $2 \mu t$

Yashas

loading... :P

Anonymous

buy jio 4g sim card :P

Anonymous

free 1 GB per day

Yashas

I dont have a mobile

3/4 loaded

Anonymous

8:11 AM

You can use jio on dongle also

Anonymous

:P

Anonymous

Jiofi

Yashas

btw I meant lambda/2 few mins ago

not lambda

pi = lambda/2

Anonymous

right

Anonymous

But there will be lambda/2 added for both the reflections

Yashas

8:12 AM

ok now I see

no

Anonymous

@Yashas Why not?

Yashas

consider a string tied at two ends

nvm

when light is reflected from a denser medium, u get extra phase difference of pi

if it is reflected from a lighter medium, u get no extra phase difference

I think string is a good example

Anonymous

So a metal is an optically denser medium than glass, isn't it?

Yashas

one end is fixed

the other end is fixed to a denser string

take a string

@blue oh interesting

did not notice that

yea, u get lambda/2 at both places then

Anonymous

Right, the solution must be wrong :/

Yashas

8:14 AM

is there zero separation b/w the metal and the glass?

In reality, there wud be some air b/w

Anonymous

I wonder....

Anonymous

No idea

Anonymous

JEE questions are very ambiguous :P

Yashas

you can fight :p

Anonymous

BTW you know there were 4-5 wrong questions in the mains paper this time

Yashas

8:17 AM

o0

Anonymous

Cp-Cv=R

Anonymous

That one

Yashas

the Cp and Cv were ambigious

Anonymous

And the kirchoff's second law and null point one

Yashas

o0

how is that wrong?

when u exchange G with E, the null point does not change

that was the answer, right?

Anonymous

8:18 AM

Firstly Kirchoff's second law can refer to both KVL and KCL

Yashas

AH

I was confused too :D

Anonymous

And secondly "null point" in itself is a very vague term

Yashas

xD

I did not know it :D

Anonymous

So that question might be cancelled

Anonymous

It was stupid

Yashas

8:19 AM

but I found the null point options, so I guessed

Anonymous

:-P

Yashas

second law to be KVL

Anonymous

Kirchoff's laws aren't named like that :/

Anonymous

Those bookworms won't undertstand

Yashas

@blue how is null point a vague term?

ok I see

null point in a wheatstone bridge

they shud have told a potentiometer or something

lol

Anonymous

8:20 AM

ok, gotta fo for lunch

Anonymous

:)

Yashas

they shud have used "the bridge is balanced" or smthing

but I think it was guessable that they meant ^ by null point

Anonymous

8:31 AM

@Yashas Yup, anyhow I am getting lesser than 250 I suppose :-P

Anonymous

I thought I would get over 250

Anonymous

So how are you preparing for advanced? :-)

Anonymous

I am redoing all my maths study materials and the physics galaxy problems

Anonymous

I am bad at organic chemistry though :/

Anonymous

Got to revise my notes and do the previous year problems

Yashas

8:34 AM

I am good with organic

I suck at inorganic

Anonymous

Opposite for me :-P

Anonymous

I'm not bad actually at organic...just that I keep forgetting the reaction mechanisms

Yashas

You don't need to remember reaction mechanisms; you can guess your way through.

Just learn the mechanism 2-3 times and you will remember it forever.

I always write the mechanism for most of the reactions.

Aldol condensation

Perkins reaction

Cannizaro

Claisen

Micheal Addition

Knovengel

Reformatskey

Beckmann

and many more

It is hard to remember tricks for each reactions

and btw aldol, perkins, claisen, etc. have the same mechanism

different names becaz u start with different products

Anonymous

@Yashas About 100 more :P

Anonymous

@Yashas Yup

Yashas

8:38 AM

if u know cannizaro and aldol, then you know all of them

aldol has acidic hydrogen

cannizaro does not use acidic hydrogen

tbh I don't know the name of the reactions

I only know aldol, cannizaro and micheal addition becaz M for active "m"methylene group

I can write the products if u give the reactants though :P

Anonymous

Aldol can occur with nitro and cyanides also :P

Yashas

yup

Anonymous

Too many exceptions

Anonymous

lol

Yashas

nitro aldol

cyano aldol

retro-aldol (reverse reaction)

those are not exceptions

same mechanism

in carbonyl compounds the C=O is making the alpha H acidic

Anonymous

8:41 AM

Right

Yashas

in CN or NO2 compounds, the CN or NO2 is making the alpha H acidic

it's the same thing

Anonymous

8:53 AM

@Yashas Does the equation $P_{net}=P_A+P_B+2\sqrt{P_AP_B} \cos(\phi)$ hold good? (Suppose we don't know the intensities of the light waves from two slits in YDSE but we know the slit powers)

Anonymous

I know that the equivalent equation for intensity holds true...not sure about this

Anonymous

Slit areas may be different

Yashas

that formula will always hold good

it is a universal formula

if you treat two source independently

and you get the intensity to be A due to the first source and B due to the second source

that formula will always give u the net intensit

Anonymous

@Yashas Which one, the power one or the intensity one?

Yashas

it is vector addition

P was power?

Anonymous

8:55 AM

P is power

Anonymous

Not intensity

Anonymous

The intensity one always holds true

Anonymous

I know that

Yashas

let me complete though, A^2 is proportional to I, replacing A^2 with I in the vector addition formula, u get that frmula

ok power

P is proportional to Intensity

so that works too

Anonymous

No wait

Yashas

8:56 AM

Intensity = power/unit area

Anonymous

P=I.A

Anonymous

If areas are different then it isn't true

Yashas

you take infinitely small A

you are talking about points

power to due to different sources at two points

Anonymous

Wait a second

Yashas

*one point

Anonymous

8:57 AM

I'm showing you the problems

Yashas

wait what the hell am I talking

I wrote nonsense

That formula won't work

becaz u meant the power of the source

Anonymous

P=Slit Power

Yashas

that is correct

Anonymous

Intensity * Area Of Slit

Yashas

8:58 AM

wot?

Anonymous

did you get the image?

Yashas

loading

Anonymous

In the image, I think the resultant power formula is wrong

Anonymous

As the slit areas will be different!

Yashas

ohhh it is correct

you need to take it this way

Anonymous

9:00 AM

@Yashas Is it?

Yashas

same intensity of light falls

the smaller slit gives out light on the other side with lower power

from the lens perspective, the intensity of light is smaller

P is proprotional to I

becaz at the lens surface area

u do P source/total area to get intensity

the total area is the same for both soruces at the lens

let me upload a pic

Anonymous

Ah, that is confusing....they mean something like Intensity= $\frac{(I.A)}{\text{Total Area}}$

Yashas

Anonymous

What is $4\pi r^2$ ?

Yashas

surface area of the virtual sphere

the power is distributed equally in all directions

in ur slit experiment, it is a hemisphere

Anonymous

9:05 AM

Ah, I see

Anonymous

Cool

Anonymous

This was a good problem then :)

Yashas

it depends on what P is

Anonymous

yup

Anonymous

P is slit power

Anonymous

9:06 AM

I.A

Anonymous

9:25 AM

Anonymous

@Yashas In interference by an air wedge, why is reflection from the lower surface of upper plate and upper surface of lower plate considered only?

Yashas

because they are not parallel

the reflection from the lower surface isn't parallel to the rays reflected from the upper surface

they don't interefere

Anonymous

@Yashas Wait, whose lower surface are you talking about?

Anonymous

The upper plate?

Yashas

the lower plate :p

ok I mixed it up lol

The rays reflected from the lower plate are not parallel to the rays reflected from upper plate

Anonymous

9:28 AM

Here they took reflection from lower surface of upper plate and upper surface of lower plate

Yashas

interesting

Anonymous

@Yashas I don't think they used that logic here...

Yashas

I might want to draw what happens inside the two plates

I'll see after few hours

Anonymous

They clearly took reflection from both the plates

Yashas

I don't have paper atm

Anonymous

9:29 AM

@Yashas You are studying on the terrace or what ?

Anonymous

:P

Yashas

garden

Anonymous

Not in your room?

Anonymous

lol

Yashas

I walk in the sun

so that I get some excersise

I wud be 24x7 inside home otherwise

Anonymous

9:30 AM

Yeah, collect some vitamin D :P

Yashas

I have an iPad though

can draw in it

too lazy

Anonymous

I study on the staircase most of the time :P

Anonymous

Passer bys look at me strangely

Yashas

need to download app and shit

Anonymous

They think I am mad, sitting with my laptop on the public stairs

Anonymous

9:32 AM

lol

Anonymous

this pg website has great problems...whew!

Anonymous

:D

Anonymous

10:22 AM

Sakazuki Akainu

1:54 PM

@Yashas ah okay

Yashas

@Yashas here is the catch. Before commenting typical Indian teacher dialogue you should get the facts right. The correct answer is C — user150700 6 mins ago

what the hell is that OP saying?

He says the correct answer given is C.

Osheen Sachdev

4:48 PM

@Yashas shifting was going on at my place so I had no internet :P

got to know yesterday night

Transcript for

Problem Solving Strategies