Lens maker formula (short derivation) | Class 12 (India) | Physics | Khan Academy
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- Опубликовано: 7 фев 2025
- Short derivation of the lens maker formula using curved surface refraction formula. This formula connects the focal length of a lens to its refractive index & the radii of curvatures. To make the derivation short, we skip using the sign conventions.
Created by Mahesh Shenoy
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
I have a doubt sir.Will that virtual image be formed in the lens? Because you told that it is in the denser medium.
@@saranyaj8643 bro still didn't got an answer 😔
People are making like 1 hour videos for this and u did it in 14 min with best explanation... that's what I need 😍
nyc
Exactly
No that's what people , no students need
Agreed
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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 😊😊☺️☺️
"object is where incident rays meet" cleared up everything
We also call that image
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!!!
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 😅
Why dont we use that
@@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
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.
This can't be any better! Beautifully explained, sir.
The way you explained ....it was amazing........we expect many more useful videos on various topics to help us ...the students.
This vedio really deserves a like ....salute ..👏👏👏👏👏👏👏
Applause...👏👏👏👏
Standing ovation...
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
CBSE should change their NCERT derivation to this.. simple and easy ! Also no need to use thin lens formula and sign convention!
How can someone dislike this!
Short, brief, and to the point. Thanks, sir.
i wanted to say , that you teach much much much better than our instituional and school teachers . ohh god , thanks for sending this gem .❤️❤️❤️❤️❤️😊
Hats off to this person
He teaches so well ! ❤️
Sir's name is Mahesh
I was waiting for the Ray optics video, infinite gratitude to you and your team
You answered all my questions. Thank you.
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.
@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
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.
The best explanation which cleared all my doubts
Woooh! amazing explanation I mean like really eye opening explanation ❤
Such a great explanation! I was struggling with the concept for the longest time. It made my concept clear! Thanks!!😄
From an Englishman, your English is very good, thanks for the helping me study for my undergraduate exam!
For an Indian?
thanks for helping me***
no... his English is good in world standard...
The best teacher in the world
You made it so simple! Thankyou so much.
good lord u r a saviour!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! i needed this really badly thankyou so so much!!!!!!!
Who are those people who disliked this video. ...??????😕😕
This is too good ☺
Best explanation with better visualisation 👌👌👌
Speechless.... What an explanation..
Best lecture on this topic i can say....
Man you're a genius
Excellent explanation. Thank you for your contribution! for the time and effort put into making this video
amazing explaination 🔥🔥🔥
Thank you, you explained it so clearly!
Now i can never forget this
After 3 days my physics term 2 exam ,this is the exact explain that i need
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😄
Same doubt bro.
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 :)
Batau bhaiya???
waaaw. the best of best videos
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??
The whole point is we don't know where the focus is.
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.
Great....👍
We can further cancel (n²-n¹)/n¹ like n²/n¹-n¹/n¹ and that is gonna be (n²/n¹)-1
Excellent sir...
Your English was amazing...🥺
U r superb....🥰
Concept clear..☺👍
It helped me😃
I love this vedio...🥰🥰🥰🥰
BEST explanation
Nice class❤
bhai kya mast teacher ho tum 🤧🤧🤧
Amazing explanation,thank you so much sir.
Amazing. Way of teaxhing bro👍👍👍👍👍
Thank you sir
Thank you
Thank you
Thank you
😊😊😊
you saved my life
this is so good
What kind of Display Board is this?
Amazing lecture ever
this is super helpful! thanks!
Brilliant.......
Thank you so much
great job!
Amazing😍😍
so we don't have to wirte that lengthy note ?
Thanks
Good explanation
Superb sir .. thank uuuu
Why the object isn't placed at infinity instead of some finite distance on the principal axis?
You can definitely place it at infinity and derive it as well :).
@@KhanAcademyIndiaEnglish Okay...thank you!
I was cleared so many doubts
Then why use sign conventions for the derivation of refraction by curved surfaces
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 :)
@@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 ?
@@KhanAcademyIndiaEnglish Thank you so much. Days' worth of confusion has been cleared in this paragraph!
7:34 🌟
R2 is supposed to be negative right? Because it is opposite to outgoing light. Someone plz clear it up
Can we use this method in boards?
awesome can i use the same in board exams.
Absolutely you can !
thank you
Very nice explanation
But the second image should be on the left side of the lens na?
Wow how did you do that???
It was really excellent
Iam really confused why the (virtual)object for the second surface is a object in the way it is!!!!
Thank you sir :)
Why these videos are not in the app?
Sir, how can i get pdf of your lecture?? 🙏🙏🙏🙏🙏
Thank you so much..
sir can we use this derivation for boards
How it acts as a virtual object
So whats the difference between lens makers equation and thin lens equation?
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
Nice explanation
Thanku
8:22 I can’t digest this fact,...
Awesome
I'm not clear about where the starting formulaco.e from
Great
Angle of incidence is not zero it is 90°
How ever derivation is good but for those who know some basics
👌👍👍👍👍
Hey in the second surface the object distance is +v.
Will it not make the formula as n1/f + n2/v.
Help
Here we don't use sign conventions its general formula ...
U should listen till end ...
Who knows what device is used to make this kind of video?
Tnx
Why can't we use normal lens formula to derive lens maker formula
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.
Nicee.
Jhakaas Sir
can someone pls tell me why we didnt use -r2 in the formula
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.
That is the most Indian accent
nice 👌 video