Question

Find focal length of a lens if it produces an image 10cm away

Answer 1

Here f= 10 cm (positive for convex lens)

m(magnification )=-3 (as image is real it will be inverted)

m=-(V/U) where V is image distance and U is object distance considering sign conventions

-3=-V/U

V=3U

Now using lens formula -1/U+1/V=1/f we get

-1/U+1/3U=1/10

-2/3U=1/10

U=-20/3=-6.66 m

So object is located at distance of 6.66m from the optical centre of lens and is located on left side of it if we consider light​ ray's travelling from left to right.