Question

9.A convex lens forms a real and inverted image of a needle at a distance of 40 cm from it. Where is the needle placed in front of the convex less if the image is equal to the size of the object? Also, find the power of the lens.​

Answer 1

For convex lens,
h
2
​

h
1
​

​
=−
u
v
​


1=−
u
v
​


u=−v

According to the question,

Using lens formula, −
50
1
​
−
50
1
​
=
f
1
​


−
50
2
​
=
f
1
​


∴f=