Question

The magnification is more than unity when object is placed at a distance d from a convex lens. Its focal length is 20 cm. What is the value of d? Options: a. Greater than 20 cm b. Less than 20 cm c. 40 cm d. Greater than 20 cm and less than 40 cm

Answer 1

`b` and `d`

Explanation:

Simply take an arbitrary value to solve the case,

Suppose magnification =`2`

Again, magnification =`v/(u)=2`

so, `v=2u`

Now,we have,

`1/v - 1/u =1/f`

so,putting the values we get,

`u=(3f)/2`

So,this is a value in between `f` and `2f` here image will be inverted.

Again we know convex lens behaves as magnifying glass when object is placed within focal length i.e `< f` but here image will be erect one.

Below is a chart for your quick memory