Question

 A 3 cm tall object is placed 18 cm in front of a concave mirror of focal length 12 cm. At what distance from the mirror should a screen be placed to see a sharp image of the object on the screen. Also calculate the height of the image formed. 

Answer 1

f= 12cm
u=18cm
height of object = 3cm(ho)
v=?

$- \frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
1/v= 1/18-1/12
1/v = -1/36
v=-36

v/u= hi/ho
hi= 36×3/18
hi=6cm
height if image = 6cm

Answer 2

f= 12cm

u=18cm

height of object = 3cm(ho)

v=?

-  \frac{1}{f}  =  \frac{1}{v}  -  \frac{1}{u}  

1/v= 1/18-1/12

1/v = -1/36

v=-36

v/u= hi/ho

hi= 36×3/18

hi=6cm

height if image = 6cm