Image Formation

Concave Mirror

Formation of image depends upon the position of the object. There are six possibilities of the position of object in the case of concave mirror.

  1. Object at infinity
  2. Object between infinity and centre of curvature (C)
  3. Object at centre of curvature (C)
  4. Object between centre of curvature (C) and Principal focus (F)
  5. Object at Principal Focus (F)
  6. Object between Principal Focus (F) and Pole (P)

Chapter List


Object at infinity:

Since parallel rays coming from the object converge at principal focus, F of a concave mirror; after reflection. Hence, when the object is at infinity the image will form at F.

object at infinity concave mirror

Fig: Object at Infinity

Properties of image:

Object between infinity and Centre of Curvature:

When object is placed between infinity and centre of curvature of a concave mirror the image is formed between centre of curvature (C) and focus (F).

object between infinity and C

Fig: Object Between Infinity and C

Properties of image:

Object at Centre of Curvature (C):

When the object is placed at centre of curvature (C) of a concave mirror, a real and inverted image is formed at the same position.

object at C concave mirror

Fig: Object at C

Properties of image:

Object between Centre of curvature (C) and Principal Focus (F):

When the object is placed between centre of curvature and principal focus of concave mirror, a real image is formed beyond the centre of curvature (C).

object between C and F concave mirror

Fig: Object between C and F

Properties of image:

Object at Principal Focus (F):

When the object is placed at principal focus (F) of a concave mirror, a highly enlarged image is formed at infinity.

object at F concave mirror

Fig: Object at F

Properties of image:

Object between Principal Focus (F) and Pole (P):

When the object is placed between principal focus and pole of a concave mirror, an enlarged, virtual and erect image is formed behind the mirror.

object between F and P concave mirror

Fig: Object between F and P

Properties of image:
Positions of Object and Image in Concave Mirror
Position of ObjectPosition of ImageSize of ImageNature of Image
At infinityAt focusPoint sized, highly diminishedReal and inverted
Between infinity and CBetween F and CDminishedReal and inverted
At CAt CSame sizeReal and inverted
Between C and FBeyond CEnlargedReal and inverted
At FAt infinityHighly enlargedReal and inverted
Between F and PBehind mirrorEnlargedVirtual and erect


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