An object is placed 12 cm away from the optical centre of a lens Its image is formed exactly midway between the optical centre and the object. Wht is the nature of lens and its focal length.
We have,
Object distance, u = -12 cm
Image distance = v
Focal length = f
Since, the image is formed midway between the lens and the object,
So, v = -6 cm
Now,
1/f = 1/v – 1/u
=> 1/f = -1/6 + 1/12
=> 1/f = -1/12
=> f = -12 cm
Thus, it is a concave lens producing a virtual image on the same side of the object.