Question

Draw neat and well labelled ray diagrams for image formation by convex lens when an object is (1) at infinity (2) beyond 2F₁ (3) at 2F₁ (4) between F₁ and 2F₁ (5) at focus F₁ (6) between focus F₁ and optical centre O. Also, in each case, state the position, nature and size of the image relative to that of the object.

Answer 1

(1) Object at infinity:

In this case, the image is formed at focus F₂ of the convex lens. It is real, inverted and highly diminished (point-sized).

(2) Object beyond 2F₁:

In this case, the image is formed between F₂ and 2F₂. It is real, inverted and diminished.

(3) Object at 2F₁:

In this case, the image is formed at 2F₂. It is real, inverted and of the same size as that of the object.

(4) Object between F₁ and 2F₁:

In this case, the image is formed beyond 2F₂. It is real, inverted and magnified (enlarged).

(5) Object at focus F₁:

In this case, the image is formed at infinity. It is real, inverted and infinitely large (highly magnified).

(6) Object between focus F₁ and optical centre O:

In this case, the image is formed on the same side of the lens as the object. It is virtual, erect and larger than the object.

[Note: Here, the image is virtual. Hence, it is shown by a dotted line.]