Class 10 Science

Image Formation by Concave Mirror

These notes are based on the chapter Light: Reflection and Refraction from class 10 science NCERT book and CBSE syllabus

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)

Object at infinity:

object at infinity concave mirror

Fig: 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.

Properties of image

  • Point sized
  • Highly diminished
  • Real and inverted

Object between infinity and Centre of Curvature:

object between infinity and C

Fig: Object Between Infinity and C

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).

Properties of image

  • Diminished compared to object
  • Real and inverted

Object at Centre of Curvature (C):

object at C concave mirror

Fig: Object at 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.

Properties of image

  • Same size as object
  • Real and inverted

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

object between C and F concave mirror

Fig: Object between C and 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).

Properties of image:

  • Larger than object
  • Real and inverted

Object at Principal Focus (F):

object at F concave mirror

Fig: Object at F

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

Properties of image

  • Highly enlarged
  • Real and inverted

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

object between F and P concave mirror

Fig: Object between F and 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.

Properties of image

  • Enlarged
  • Virtual and erect

Positions of Object and Image in Concave Mirror

  • Object at infinity: Image is formed at focus, image is real, inverted, point sized and highly diminished.
  • Object between infinity and C: Image is formed between F and C, image is real, inverted and diminished in size
  • Object at C: Image is formed at C, image is real, inverted, and of same size as object
  • Object between C and F: Image is formed beyond C, image is real, inverted and enlarged
  • Object at F: Image is formed at infinity, image is real, inverted and highly enlarged
  • Object between F and P: Image is formed behind the mirror, image is virtual, erect and enlarged

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