Class 10 Physics



Image Formation by Convex Lens

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

  • Object at infinity
  • Object beyond centre of curvature, C
  • Object at centre of curvature, C
  • Object between centre of curvature, C and principal focus, F
  • Object at principal focus, F
  • Object between principal focus, F and optical centre, O

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 F2.

object at infinity convex lens

Fig: Object at Infinity

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

Object beyond centre of curvature, C1 or 2F1:

A diminished, real and inverted image is formed between principal focus, F2 and centre of curvature, C2 at the opposite side when an object is placed beyond C1 of a convex lens.

object beyond 2F convex lens

Fig: Object Beyond 2F

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

Object at centre of curvature, C1 or 2F1:

A same sized, real and inverted image is formed at centre of curvature, C2 when object is placed at centre of curvature, C1 of a convex lens.

object at 2F convex lens

Fig: Object at 2F

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


Object between centre of curvature, C1 and principal focus, F1:

An enlarged, real and inverted image is formed beyond centre of curvature, C2 when an object is placed between centre of curvature, C1 and principal focus, F1 of a convex lens.

object between F2 and F convex lens

Fig: Object between 2F and F

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

Object at principal focus, F1:

An infinitely large, real and inverted image is formed at infinity when object is placed at principal focus, F1 of a convex lens.

object at focus convex lens

Fig: Object at F

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

Between principal focus, F1 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, F1 and optical centre, O of a convex lens.

object between F and O convex lens

Fig: Object between F and O

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