Question

1. An object is placed 20cm from a concave lens of
focal length 10cm . Find the image formed by the
long.

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Answer 1

Given f = - 20 cm, (sign convention) , v = - 10 cm

(∴ image formed by concave lens is virtual)

By using lens formula, 



or u = - 20 

Thus the object is placed at 20 cm from the concave lens  

    

Here is ur answer

Answer 2

$\huge{\boxed{\red{\bf{Kris \: Wu:-}}}}$

Focal length of concave mirror, f = -20 cm

Distance of object from the mirror, u = -10 cm

use formula, 1/v + 1/u = 1/f

or, 1/v = 1/f - 1/u

or, 1/v = 1/-20 - 1/-10

or, 1/v = -1/20 + 1/10 = 1/20

or, v = +20cm

hence, image position is the 20cm right side from the pole of the concave mirror as shown in the diagram. The image is straight and bigger than the object.

${\huge{\fcolorbox{white}{WHITE}{♡HAN JU HUI♡}}}$