Lens maker formula (short derivation) | Class 12 (India) | Physics | Khan Academy

[@saranyaj8643]

I was searching for lens makers formula for the past 3 days....though i went through many this is the best which was ultimately clear and simple...thank you so much

[@saranyaj8643]

I have a doubt sir.Will that virtual image be formed in the lens? Because you told that it is in the denser medium.

[@internetuser2845]

People are making like 1 hour videos for this and u did it in 14 min with best explanation... that's what I need 😍

[@AmazingAI7861]

nyc

[@kaushikb2819]

Exactly

[@nelsonberkson2275]

No that's what people , no students need

[@canyoukillme612]

Agreed

[@AnandYadav-bt6or]

That's why khan academy is my favourite

[@anchalverma3119]

The person who is teaching seems so happy after explaining each line which itself is a great source of motivation. Loved the way you teach 😊😊☺️☺️

[@nandiniagrawal42]

"object is where incident rays meet" cleared up everything

[@Exhilarated1750]

We also call that image

[@hiteshattri611]

They are the only one who are providing real education free of cost they explain each and every thing very nicely no extra watch time,no deceiving, small videos straight to the point pure THANKS YOU KHAN ACADEMY!!!

[@vishank7]

This can't be any better! Beautifully explained, sir.

[@mrinalkantighosh9434]

The way you explained ....it was amazing........we expect many more useful videos on various topics to help us ...the students.

[@arvindsivakumar4818]

13:03 "Why don't we use sign conventions?" The question none explained you made it easy to understand. Thanks Edit: This derivation came in my exam and I got it right. Thank you again. I even wrote why we dont use sign conventions 😅

[@danielnoah2024]

Why dont we use that

[@zelaa6154]

​​@@danielnoah2024tbh we do use sign convention when we derive equations right, all this time, I'd like to think that we have indeed used Cartesian sign convention and measure the lengths from the optical centres in here (since there's two curved surfaces the direction in which we will have to measure distance towards the optical centre differs) and heights of objects and images are not required for this lens maker formula there was no need to change signs at all. So if what he said is true we have to change signs in this formula only when we're solving problems where we measure distance from the objects or images to the optical centre. sorry for this rant >_< I just hope this is how it works

[@GowthamPhysics]

Lens makers formula is not derived for a particular type of lens but is derived as general formula valid for any type of lens. Hence sign convention is not followed while deriving Lens maker's formula.

[@fammy3241]

How can someone dislike this!

[@FUNnMORALS]

Nice explanation with diagram.Till now I not understand the lens makers formula but by seeing this video I got a full clarity of lens makers formula . Now I can derive this formula very easily by your explanation.Thank you

[@thehugibugi8602]

This vedio really deserves a like ....salute ..👏👏👏👏👏👏👏 Applause...👏👏👏👏 Standing ovation...

[@Somelions2]

CBSE should change their NCERT derivation to this.. simple and easy ! Also no need to use thin lens formula and sign convention!

[@ヴィネット-l3z]

Short, brief, and to the point. Thanks, sir.

[@taanisharora5577]

3:28 intuitively, it makes sense for the focus to be at I because thats where the parallel ray would've met the other incident ray after refraction. an interesting observation here that the focus doesn't have any definition other than just a point at which two parallel rays meet after refraction no matter how many times it gets refracted.

[@rishitiwari4625]

@a nutty lemur I assure you the most offended people from this thread are the ones who stumble across you attempting to have a normal conversation with somebody and now their day is ruined

[@tamanna982]

i wanted to say , that you teach much much much better than our instituional and school teachers . ohh god , thanks for sending this gem .❤️❤️❤️❤️❤️😊

[@anishatadkod1778]

Hats off to this person He teaches so well ! ❤️

[@nirensarkar7197]

Sir's name is Mahesh

[@devanshithakkar2461]

I was waiting for the Ray optics video, infinite gratitude to you and your team

[@MrIncendiarySquirrel]

From an Englishman, your English is very good, thanks for the helping me study for my undergraduate exam!

[@chetnagreesan8747]

For an Indian?

[@anarchist28]

thanks for helping me***

[@tinydoge570]

no... his English is good in world standard...

[@tapassarkar2015]

Thank u very much sir... I have been studying in Khan Academy for 2 years and I am very much pleased with your teaching. In physics I understands only your lectures. So I want more videos from you. Khan Academy is the best app for building concepts.But I think it would be more helpful if we get a chance to clear our doubts by directly connecting with you.I love the way of presenting practical images, done by you. I expect such awesome videos in chemistry and biology too.

[@rohilsaraf8422]

You answered all my questions. Thank you.

[@mrinalkantighosh9434]

The best explanation which cleared all my doubts

[@rtsp4800]

Isn't the ray which passes through F the incident ray? Or is it the refracted ray? Because doesn't the incident ray pass through the focus? Please explain.

[@Rose-xq5wx]

Woooh! amazing explanation I mean like really eye opening explanation ❤

[@just_a_wholesome_panda]

Such a great explanation! I was struggling with the concept for the longest time. It made my concept clear! Thanks!!😄

[@physicsgyan9694]

Who are those people who disliked this video. ...??????😕😕 This is too good ☺ Best explanation with better visualisation 👌👌👌

[@MahiMahi-zw5im]

Plz clarity my doubt--- when you considered only ane surface of the lens,the parallel incident ray met optical axis beyond the center of curvature after refraction.. But whatever the curved surface(may be 1 curved surface or biconvex) the parallel ray should meet the focus.. Then why it touches optical axis beyond c??

[@KhanAcademyIndiaEnglish]

The whole point is we don't know where the focus is.

[@sweetyghosh]

Speechless.... What an explanation.. Best lecture on this topic i can say....

[@lrajarathinam]

What kind of Display Board is this?

[@MARYAM-ed9si]

You made it so simple! Thankyou so much.

[@himanishbugudala2393]

We can further cancel (n²-n¹)/n¹ like n²/n¹-n¹/n¹ and that is gonna be (n²/n¹)-1

[@prakharshrivastava8649]

good lord u r a saviour!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! i needed this really badly thankyou so so much!!!!!!!

[@the_sophile]

Excellent explanation. Thank you for your contribution! for the time and effort put into making this video

[@0soinspiring694]

bhai kya mast teacher ho tum 🤧🤧🤧

[@cherikarengh005]

so we don't have to wirte that lengthy note ?

[@furiousarpan7473]

The best teacher in the world

[@udayammanikumaran9744]

waaaw. the best of best videos

[@bharathtej2408]

Iam really confused why the (virtual)object for the second surface is a object in the way it is!!!!

[@vishank7]

Hoping somebody could help me with this one. In the derivation for refraction from a curved surface, we used sign convention to generalize the cases, such that they apply to each and every case(Watch Mahesh sir's vid on the same). But here, we are doing the exact opposite by not using it! Any help would be appreciated😄

[@rohitptnk03]

Same doubt bro.

[@ishanrai1227]

Think of sign convention as a way to transform a "general equation" (that work for all cases like say for both concave or convex) into a "specific equation" (whatever situation we have at hand) and vice versa. For the curved surface we derive for a specific case right? Then to generalise it we use sign conventions. In this derivation we can also use signs. If we do we end up using it twice. Let's see how. First we are applying the general curve refraction formula for our specific case, so we need to use signs. (First time). Finally after deriving everything, we would have derived the lens makers formula for A SPECIFIC CASE (bi convex lens in our example). So to make it a general formula we need to AGAIN apply sign convention. (Second time). Applying sign conventions twice is like multiplying with negative 1 twice which has no over all effect on sign. And so to make the process a little less tedious I didn't use signs :)

[@jayparas7627]

Batau bhaiya???

[@mephistopheles7986]

Now i can never forget this

[@tanviakhtar1527]

R2 is supposed to be negative right? Because it is opposite to outgoing light. Someone plz clear it up

[@20_SinManya]

Why the object isn't placed at infinity instead of some finite distance on the principal axis?

[@KhanAcademyIndiaEnglish]

You can definitely place it at infinity and derive it as well :).

[@20_SinManya]

@@KhanAcademyIndiaEnglish Okay...thank you!

[@sweetyghosh]

Sir, how can i get pdf of your lecture?? 🙏🙏🙏🙏🙏

[@Piyushverma2578]

After 3 days my physics term 2 exam ,this is the exact explain that i need

[@UnnaHope]

Thank you, you explained it so clearly!

[@anweshkrishnab]

Your English was amazing...🥺

[@rishuartist]

amazing explaination 🔥🔥🔥

[@chimwemwegerald8745]

Man you're a genius

[@mouneshsanju7898]

Excellent sir...

[@pritipadmadas3494]

U r superb....🥰 Concept clear..☺👍

[@swapandas17]

Why these videos are not in the app?

[@botmanvirusanti]

But the second image should be on the left side of the lens na?

[@VG__]

7:34 🌟

[@saubhagya7579]

Thank u bhai. Dil se❤️

[@Gopal-lq5rm]

Amazing. Way of teaxhing bro👍👍👍👍👍

[@lakshmikanthhn-vt7bo]

Great....👍

[@mustakimkhan8021]

It helped me😃

[@hachemouanes8751]

you saved my life

[@prakasams529]

Then why use sign conventions for the derivation of refraction by curved surfaces

[@KhanAcademyIndiaEnglish]

Think of sign convention as a way to transform a "general equation" (that work for all cases like say for both concave or convex) into a "specific equation" (whatever situation we have at hand) and vice versa. For the curved surface we derive for a specific case right? Then to generalise it we use sign conventions. In this derivation we can also use signs. If we do we end up using it twice. Let's see how. First we are applying the general curve refraction formula for our specific case, so we need to use signs. (First time). Finally after deriving everything, we would have derived the lens makers formula for A SPECIFIC CASE (bi convex lens in our example). So to make it a general formula we need to AGAIN apply sign convention. (Second time). Applying sign conventions twice is like multiplying with negative 1 twice which has no over all effect on sign. And so to make the process a little less tedious I didn't use signs :)

[@nitink9879]

@@KhanAcademyIndiaEnglish If we had used sign coventions at 9:19 it would have been (n1/f) - (n2/v) = (n2 - n1)/ (-R2) .And finally I have to apply sign conventions again to generalise the equation. Am I right sir ? And is this the only sign convention that has to be applied to specify the equation for convex lens ? Or is there any other sign conventions to be applied in addition to this ?

[@niranjan7457]

@@KhanAcademyIndiaEnglish Thank you so much. Days' worth of confusion has been cleared in this paragraph!

[@mouneshsanju7898]

I was cleared so many doubts

[@dr.shilpamathapathi6033]

Can we use this method in boards?

[@lenzlaw3584]

I love this vedio...🥰🥰🥰🥰

[@koushikr8196]

How it acts as a virtual object

[@janhavisoni1559]

Amazing explanation,thank you so much sir.

[@minakshithakur8918]

Thank you sir

[@reejaamin9641]

I'm not clear about where the starting formulaco.e from

[@vik0_052]

sir can we use this derivation for boards

[@keshabdeb4767]

Thank you Thank you Thank you 😊😊😊

[@SokaGoshos24]

BEST explanation

[@rohitptnk03]

Hey in the second surface the object distance is +v. Will it not make the formula as n1/f + n2/v. Help

[@thehugibugi8602]

Here we don't use sign conventions its general formula ... U should listen till end ...

[@piglink10]

So whats the difference between lens makers equation and thin lens equation?

[@PavnikSai]

Lens maker's equation is used to make a lens when a combination of the focal length, radii, refractive indices are given. Lens equation can tell us the focal length or v or u when a combination of them is given

[@brontokill199]

Amazing lecture ever

[@shambhavisingh982]

Amazing😍😍

[@licmpm1129]

Wow how did you do that???

[@vivlodia]

this is super helpful! thanks!

[@prishas6151]

can someone pls tell me why we didnt use -r2 in the formula

[@rtsp4800]

He did not use sign convention as he later says that this formula is derived for general use and not for specific use. You can later use sign convention while substituting values in numericals.

[@fadhil2280]

Nice class❤

[@ishantripathi9707]

great job!

[@lrajarathinam]

Brilliant.......

[@sganju5998]

Superb sir .. thank uuuu

[@Tanveermalik011]

awesome can i use the same in board exams.

[@mainakdeb9188]

Absolutely you can !

[@Tanveermalik011]

thank you

[@Saii12]

this is so good

[@pleasant_gazelle]

Thanks Good explanation

[@balajothiadithya3144]

Thank you so much

[@krishnaphysics4102]

Very nice explanation

[@samiransaha5739]

It was really excellent

[@anupchavan4346]

8:22 I can’t digest this fact,...

[@vispelliarmus]

Thank you sir :)

[@samiransaha5739]

Why can't we use normal lens formula to derive lens maker formula

[@adityanair7342]

Because the regular lens formula is derived AFTER you derive this formula. The NCERT textbook for class 12 Physics (Volume II) has a neat derivation that hits two birds with the same arrow. The lens maker's formula and the thin lens formula are derived one after the other at one go.

[@abdulrahimp1759]

Thanku

[@khamisfarid3804]

Who knows what device is used to make this kind of video?

[@vr9722]

Thank you so much..

[@educationalguru6912]

Jhakaas Sir

[@SimratDeol20]

Perfect explanation.. Thanks😁

[@sikharabhilekhgogoi6594]

Nice explanation

[@Differendramovies]

Great

[@agam0167]

That is the most Indian accent

[@sudhanvab]

Awesome

[@oyeemahendra]

I couldn't understand somewhere is 1/r1+1/r2 and somewhere 1/r1-1/r2

[@adityanair7342]

the formula with the plus has taken care of the sign convention completely and requires r1 and r2 to be the *magnitudes* (ie, modulus) of whatever the distance from the centres are. Whereas with this formula you need to take care of the sign convention WHILE you apply the formula.

[@minakshithakur8918]

👌👍👍👍👍

[@nangsanbhalangblah333]

Nicee.