nyc

Exactly

No that's what people , no students need

Agreed

That's why khan academy is my favourite

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

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

😅sorry to say I can't understand can u put it simply

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.

Sir's name is Mahesh

@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

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

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???

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

For an Indian?

thanks for helping me***

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

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

@@KhanAcademyIndiaEnglish Okay...thank you!

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

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!

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.

Absolutely you can !

thank you

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.