Question

©An object 5.0 cm in height is placed at the distance of 20cm in front of convex lens of focal length 10 cm .Find position , size and nature of the image

#10 point

Answer 1

here,
height of object = h1 = 5.0cm=5cm
 u= -20cm
f=10cm
as per lens formula                            
1/v-1/u = 1/f  
=> 1/v = 1/f + 1/u
=> 1/v = 1/10 +(-1/20)
=>1/v = 1/10 - 1/20
=> 1/v =(2-1)/20   .... lcm of 10,20 = 20
=> 1/v = 1/20 
=> v= 20cm 
the image formed is real and inverted and of the same size as the object i.e object is placed at 2f1 and image is formed at 2f2

Answer 2

Given that

Object distance u = 20cm
Image distance ,v = ?
Focal length ,f = 10cm

h1 = 5.0cm

putting this values in the lens formula

1/v - 1/u = 1/f

we get :

1/v - 1/20 = 1/10

1/v = 1/10 - 1/20

1/v = 2- 1/20

1/v = 1/20

image distance, v = + 20

Magnifications ,m = v/u

m = 20/20

m = 1

then m = h2/h1

1 = h2/5

h2 = 5

the image image is formed by real and inveterd .