An object is kept at a distance of 100 cm from each of the above lenses.

Calculate the

(a) image distance and

(b) magnification in each of two cases.

(a) Given

Object distance (u) = -100cm

Focal length (f) = 50cm

Image distance = v

By lens formula;

⇒ v=100cm

Hence the image is formed at 100 cm behind the lens.

Object distance (u) = -100cm

Focal length (f) = -25cm

Image distance = v

By lens formula;

⇒ v =

⇒ v= -20cm

Hence the image is formed at 20cm in front of the lens.

(b) For 1st case

Object distance (u) = -100cm

Image distance (v) = 100cm.

By Magnification Formula

Magnification (m) =

⇒ Magnification =

Therefore, Magnification for the 1st case is -1. The negative sign means the image is real and inverted.

For 2nd case

Object distance (u) = -100cm

Image distance (v) = -20cm.

By Magnification Formula

Magnification (m) =

⇒ Magnification =

Therefore, Magnification for 2nd case is 0.2. The positive sign means the image is erect and virtual.