When light rays from the sun fall on a convex lens along a direction paralle to its axis

The rays of light falling on a convex lens in a direction parallel to principal axis of the lens, get refracted through the lens and meet actually at a single point F on the principal axis of the lens. This point is called principal focus of the lens. Read the above passage and answer the following questions : (i) Is principal focus of a convex lens, a real point ? Is the same true for a concave lens ? (ii) A distinct image of a distant tree os obtained on a screen held at 40 cm from a convex lens. What is its focal length ? (iii) Our teachers and parants advise us to stay focussed. What does it imply ?

Rays of light from Sun falls on a biconvex lens of focal length f and the circular image of Sun of radius r is formed on the focal plane of the lens. Then

Converging light rays are falling on a convex lens. If the focal length of the lens is 30 cm, then find the position of the image.

Rays of light from Sunn falls on a biconvex lens of focal length f an the circular image of Sun of radius r is formed on the focal plane of the lens. Then,