The figure shows an object AB and lens L.let the two focii are virtual erect and diminished.
1.draw a ray of light starting through A and passing throughO.show how it emerges.
2.locate and state the final image formed
Answers
When an object is placed at infinity, the rays coming from it are parallel to each other. Let us consider two rays, one striking the mirror at its pole and the other passing through the center of curvature. The ray which is incident at the pole gets reflected according to the law of reflection and the second ray which passes through the center of curvature of the mirror retraces its path. These rays after reflection form an image at the focus. The image formed is real, inverted and diminished.
The image is
At F
Real
Inverted
Diminished
Concave Mirror Image
When the Object is Placed beyond C :
The two rays which are considered to obtain the image are :
A ray passing through the center of curvature
A ray parallel to the principal axis. The ray passing through the center of curvature retraces its path and the ray which is parallel to the principal axis passes through the focus after reflection. These rays after reflection meet at a point between C and F. The image is inverted, real and diminished
The image is
Between C and F
Real
Inverted
Diminished
Concave Mirror Diagram
When the Object is Placed at the Center of Curvature:
Consider the two rays, one parallel to the principal axis and the other passing through the focus. The ray of light which is parallel to the principal axis passes through the focus after reflection. The other ray passing through the focus after reflection emerges parallel to the axis. After reflection these rays meet at the center of curvature to form an inverted image, which is real and of the same size as the object.
The image is
At C
Real
Inverted
Same size as object
Concave Mirror Images
When the Object is between C and F :
Here we consider a ray of light which is parallel to the principal axis and another ray passing through the focus. The ray which is parallel to the principal axis passes through the principal focus and the ray which passes through the focus after reflection emerges parallel to the principal axis. The reflected rays meet at a point beyond C and the image is real, inverted and magnified.
The image is
Beyond C
Real
Inverted
Magnified
Image in Concave Mirror
When the Object is between C and F :
Let us consider a ray of light which is parallel to the principal axis and another ray passing through the center of curvature. The ray which is parallel to the principal axis passes through the focus and the ray which passes through the center of curvature retraces its path. The reflected rays are parallel to each other, and would meet only at infinity i.e., the image is formed at infinity and it is a real, inverted, enlarged image of the object.
The image is
At infinity
Real
Inverted
Magnified
Image Formed by Concave Mirror
When the Object is between the Pole and the Focus :
Considering a ray of light which is parallel to the incident ray and another ray which is passing through the center of curvature. The ray which is passing through the center of curvature retraces its path and the other ray which is parallel to the principal axis after reflection passes through the focus. These rays appear to meet behind the mirror when the reflected rays are extended backwards. The image is virtual, erect and magnified.