Question

An object is placed 20 cm from the concave lens. Focal length of
the lens is 30 cm .Then find the image distance ​

Answer 1

Explanation:

1/u - 1/v=1/f

1/(-20) - 1/v=1/(-30)

-1/20+1/30=1/v

-3+2/60=1/v

-1/60=1/v

v=-60

Answer 2

Answer:

-12 cm

Explanation:

u = 20 cm

focal length of concave lens= 30 cm

f= -30 cm

we know that from the lens formula

$\frac{1}{f} = \frac{1}{u} +\frac{1}{v}$

$\frac{1}{-30} = \frac{1}{20} +\frac{1}{v}$

solving the above equation we get

$\frac{1}{v} = -\frac{1}{20} -\frac{1}{30}$

v= -60/5= -12 cm