Question

concave lens forms the image of an object kept at a distance 20 CM in front of it at a distance 10 cm and the size of the object draw the image for it​

Answer 1

Getting the magnification:

(20cm)/(-10cm)=(img-obj)/(img-L)

=(img-L+L-obj)/(img-L)

=1-(obj-L)/(img-L)

= 1–1/M

-> M = 1/3

Getting the focal length/power

M=1-p(img-L)

1/3 = 1-p(-10cm)

p = -1/15cm

f = 1/p = -15cm

i think this is the answer