Question

Draw labelled ray diagrams to illustrate the differences between the virtual
images formed by using (a) a concave lens (b) a convex lens.
​

Answer 1

Below one is a concave lens. Here:-

• When an object is placed at infinity, a virtual image is formed at the focus. The size of the image is much smaller than that of the object.
• When an object is placed at a finite distance from the lens, a virtual image is formed between the pole and the focus of the convex lens. The size of the image is smaller than that of the object.

in the above part, the right one shows the virtual image:-

• When an object is placed in between focus and pole, a virtual image is formed. The size of the image is larger than that of the object.

Point to be remembered:-

A virtual, erect and diminished image is always formed in a concave lens.

Answer 2

Explanation:

( a ) Concave lens always forms virtual image.

( b ) Convex lens forms real image for 1st 5 positions of the object and forms virtual image for the 6th position.

For Convex lens

1st 5 positions :

For Object

( i ) At infinity

( ii ) Beyond C1

( iii ) At C1

( iv ) Between F1 and C1

( v ) At F1

For Image

( i ) At F2

( ii ) Between F2 and C2

( iii ) At C2

( iv ) Beyond C2

( v ) At infinity

6th position :

For Object

( vi ) = Between F1 and O

For Image

( vi ) = Behind the lens