Rules for Obtaining Image formed by concave Mirrors
The image is formed at that point where at least two reflected rays intersect ( or Appear to intersect ).
Rule 1. If the incident light ray is parallel to the principal axis , then the reflected Ray passes through the focus.
Rule 2. If the incident light ray passes through the focus , the reflected Ray becomes parallel to the principal axis.
Rule 3. If the light ray is incident at the pole of a concave mirror is reflected back making the same angle with the principal axis.
Rule 4. If the incident light ray passes through the centre of curvature of a concave mirror is reflected back along the same path.
Formation of Different Types of Images By a concave Mirror:
The type of image formed by a concave mirror depends on the position of object in front of the mirror.
Case 1 : when an object is at Infinity from a concave mirror , the image formed is :
(i) At the focus (F).
(ii) Real and inverted
(iii) Much smaller than the object ( Highly Diminished ).
Case 2. When the object is beyond the centre of curvature of the concave mirror , the image formed is :
(i) Between the focus and centre of curvature. C/F
(ii) Real and inverted.
(iii) Smaller than the object and Diminished.
Case 3. When the object is placed at the centre of curvature of a concave mirror (object at C) , the image formed is
(i) At the centre of curvature (C).
(ii) Real and Inverted.
(iii) Same size as the object.
Case 4. When the object is placed between focus and centre of curvature ( Object between F and C ) , the image formed is :
(i) Beyond the centre of curvature.
(ii) Real and Inverted.
(iii) Larger than the object and Magnified.
Case 5. When the object is placed at the focus of a concave mirror ( Object at F) , the image formed is :
(i) At infinity.
(ii) Real and Inverted.
(iii) Highly Magnified.
Case 6 : When object is placed between pole and focus of the mirror ( Object P and F) , the image formed is :
(i) Behind the mirror.
(ii) Virtual and Eract.
(iii) Larger than the object and Magnified.
