# I asked this just before 5 minutes but the answer was given 1/v-1/u= 1/f but the formulae of convex mirror is 1/v+1/u=1/f1.  A convex lens has a focal length of 10 cm. At what distance from the lens should the object be placed so that it forms a real and inverted image 20 cm. away from the lens? What would be the size of the image formed if the object is 2 cm high? With the help of a ray diagram show the formation of the image by the lens in this case?

Dear Student ,
Kindly read the question carefully here in this particular question lens is used not a mirror .
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• 1
1/f =1/v -1/u
1/10 = 1/20 - 1/u
1/20 - 1/10 = 1/u
-1/20 = 1/ u
u = - 20cm

hi/ho = v/u
hi/2= 20 / -20
hi = -2 cm

DRAW DIAGRAM
• 2
f=10cm 2f=20cm V=20cm 1/f=1/v - 1/u 1/10=1/20 -1/u 1/u=1/20 - 1/10 1/u=1/20 - 2/20 1/u=-1/20 u= -20cm
• 1
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