Question

an object is placed at 30 cm in front of concave lens of focal length 10 cm. at what distance from the lens image is formed​

Answer 1

Answer:

f = - 25 cm

​v = ?

By lens formula

1/f = 1/v - 1/u

1/-25=1/v - 1/-25

1/-25 = 1/v + 1/25

1/v = -2/25

v = -25/2

v = - 12.5 cm

The negative sign shows that the image is erect and virtual.

If the image and object are on the same side of the lens, the image distance is negative and the image is virtual.

Answer 2

Given:-

object distance :- -30cm

focal length :- -10cm

1/f=1/u + 1/v

=> 1/v= 1/f - 1/u

=> 1/v = 1/(-10) + 1/(-30)

=>1/v = -{ 1/10+1/30}

=>1/v = - { (3+1)/30}

=>1/v = - {4/30}

=>1/v= - {2/15}

or,

v=-15/2cm

hence, image distance = 15/2cm

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