Question

Describe the characteristics of the image formed when the object is placed at $2{F_1}$ of the concave lens.

Answer 1

The object is placed at a distance $2{F_1}$ from the pole of the concave lens. The point corresponding to this distance is the centre of curvature of the lens on its left.

Complete step by step answer.
Step 1: Sketch a figure representing the image formation of the object placed at $2{F_1}$ of the concave lens.

Image formation in a concave lens

Step 2: Describe the image formed.
All images formed by the concave lens are diminished and virtual. From the above figure, we see that the image formed is upright too. It is located just before the first focal point ${F_1}$ of the lens.

Additional information: A concave lens is thinner at its centre and has bulging edges. A concave lens is also known as a diverging lens as the light rays diverge after refraction. Concave lenses find many applications in real-life. A concave lens is usually used to correct short-sightedness of the eye as it can shift the light rays coming from the object back at the retina. The diverging property of the concave lens is also used in binoculars as it makes the objects look smaller in size and farther away.

Note: For the image formation, the rays of light from the object are taken such that a ray passing parallel to the principal axis will diverge upon refraction, a ray passing through the optical centre of the lens passes undeflected upon refraction and a ray of light appearing to meet the principal focus will emerge parallel to the principal focus upon refraction.