Question

an object is placed at a distance of 15 cm from a concave lens of focal length 30 cm list four characteristics (nature position etc.) of the image formed by the lens

Answer 1

u=-30cm   f= -15cm  

1/f=1/v-1/u

1/v=1/f+1/u

on substituting  v=-10cm

m=v/u

m=-10/-30

m=1/3=.33

so the magnification is positive so it is a virtual erect image .

m isless  than 1 so the image is  diminished .

and v is negative so the image is formed on the same side of the lens.

Answer 2

1/f = 1/v - 1/u
1/30 = 1/v - 1/15
1/v = 1/30 +1/15
= 1+2/30
= 3/30
=1/10
v = 10
the image formed at a distance of 10 cm