Theory:

Let us now find the position, size and nature of the image by drawing the ray diagram for a small linear object placed on the principal axis of a concave mirror at different positions.
 
Case-I: When the object is placed at infinity, the rays of light reaching the concave mirror is parallel to each other.
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Position of the Image: The image is formed at the principal focus \(F\).
Nature of the Image: Real, inverted and highly diminished in size.
 
Case-II: When the object is placed beyond the centre of curvature.
 
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Position of the image: Between the principal focus \(F\) and centre of curvature \(C\).
Nature of the image: Real, inverted and smaller than an object.
 
Case-III: When the object is placed exactly at the centre of curvature.
 
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Position of the image: The image is at the centre of curvature itself.
Nature of the image: Real, inverted, and same size as the object.
 
Case-IV: When the object is placed between the centre of curvature \(C\) and principal focus \(F\).
 
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Position of the image: The image is beyond \(C\).
Nature of the image: Real, inverted and magnified.
 
Case-V: When the object is placed at the principal focus \(F\).
 
Position of the image: The image is beyond at infinity.
Nature of the image: Real, inverted and magnified.
 
 
Case-VI: When the object is placed between the focus \(F\) and the pole \(P\).

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Position of the image: The image is behind the mirror.
Nature of the image: Virtual, erect and magnified.