Question

how can we find out the focus of a lens ?? plz explain in detail ....

Answer 1

you can form the image of a very far object on screen . adjust it's position so that the image is sharp . the distance between the lens and screen is focal length

Answer 2

Hello friend
You can find focus of a lens using lens formula,
1/f=1/v-1/u
Where, v = Distance of image from optical centre of lens
u = Distance of object from optical centre of lens
and f = Focal length of lens .


The lens formula is applicable both in convex lenses and concave lenses.
First of all you should use sign conversation to find the signs of v , u.then you have to put all these values in the above equation.after that you will get your answer.