Image Formation by 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.
- Object at infinity
- Object between infinity and 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 Pole (P)
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.
Fig: Object at Infinity
Properties of image:
- Point sized
- Highly diminished
- Real and inverted
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).
Fig: Object Between Infinity and C
Properties of image:
- Diminished compared to object
- Real and inverted
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.
Fig: Object at C
Properties of image:
- Same size as object
- Real and inverted
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).
Fig: Object between C and F
Properties of image:
- Larger than object
- Real and inverted
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.
Fig: Object at F
Properties of image:
- Highly enlarged
- Real and inverted
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.
Fig: Object between F and P
Properties of image:
- Enlarged
- Virtual and erect
| Positions of Object and Image in Concave Mirror | |||
|---|---|---|---|
| Position of Object | Position of Image | Size of Image | Nature of Image |
| At infinity | At focus | Point sized, highly diminished | Real and inverted |
| Between infinity and C | Between F and C | Dminished | Real and inverted |
| At C | At C | Same size | Real and inverted |
| Between C and F | Beyond C | Enlarged | Real and inverted |
| At F | At infinity | Highly enlarged | Real and inverted |
| Between F and P | Behind mirror | Enlarged | Virtual and erect |