Question

An object is placed at a distance of 25 cm from a concave lens of focal length 10 centimetre find the position of image

Answer 1

According to the lens formula

1/v-1/u=1/f

v=image distance

u= object distance

f= focal length

now this distances are always measured from the pole and if it is direction vector is in the direction of light's path then the distance is positive and if it is opposite to light's pathway then it is negative.

Now from the equation we can write

1/v -1/(-25)=1/(-10)

1/v= -1/25-1/10= -(2/50+5/50)

1/v= -7/50

v= -50/7 cm

image is situated at -50/7 cm from lens