Question

Discuss the methods of image tracing in convex lens and concave lens.

Accepted Answer

Image Formation by Convex Lens:

There are six possibilities of position of object in the case of convex lens:

Object at infinity: Convex lens converge parallel rays coming from objet at infinity and a highly diminished - point sized, real and inverted image is formed at principal focus $F 2$ .

Properties of Image: Image is highly diminished, real and inverted.

Object beyond centre of curvature, $C 1$ or $2 F 1$ : A diminished, real and inverted image is formed between principal focus, $F 2$ and centre of curvature, $C 2$ at the opposite side when an object is placed beyond $C 1$ of a convex lens.

Properties of Image: Image is diminished, real and inverted.

Object at centre of curvature, $C 1$ or $2 F 1$ : A same sized, real and inverted image is formed at centre of curvature, $C 2$ when object is placed at centre of curvature, $C 1$ of a convex lens.

Properties of Image: Image is same size as object, real and inverted.

Object between centre of curvature, $C 1$ and principal focus, $F 1$ : An enlarged, real and inverted image is formed beyond centre of curvature, $C 2$ when an object is placed between centre of curvature, $C 1$ and principal focus, $F 1$ of a convex lens.

Properties of Image: Image is enlarged, real and inverted.

Object at principal focus, $F 1$ : An infinitely large, real and inverted image is formed at infinity when object is placed at principal focus, $F 1$ of a convex lens.

Properties of Image: Image is highly enlarged, real and inverted.

Between principal focus, $F 1$ and optical centre, $O$ : A virtual, erect and enlarged image is formed at the same side of lens, when an object is placed between principal focus, $F 1$ and optical centre, $O$ of a convex lens.

Properties of Image: Image is enlarged, virtual and erect.

Image Formation by Concave Lens:

There are only two possibilities of position of object in the case of a concave lens:

Object is at infinity: A highly diminished point sized, virtual and erect image is formed when object is at infinity by a concave lens at principal focus $F 1$ .

This figure shows a concave lens. Light rays are parallel to the principal axis which shows that they are coming from infinity. After passing through the lens, light rays diverge from the lens and appear to be coming from the focus. That is why image is formed on the focus of the lens.

Properties of Image: Image is point sized, highly diminished, virtual and erect.

Object is between optical centre, $O$ and infinity: A diminished, virtual and erect image is formed between principal focus $F 1$ and optical centre, $O$ , when object is placed between optical centre and infinity of a concave lens.

This figure shows a concave lens. One of the rays of light is parallel to the principal axis and another ray of light is passing through the optical centre of lens. When both the emergent rays are drawn backwards they appear to be intersecting somewhere between $F$ and $O$ .

Properties of Image: Image is diminished, virtual and erect.

Discuss the methods of image tracing in convex lens and concave lens.

Important Questions on Ray Optics and Optical Instruments

Learn and Prepare for any exam you want !