Rules For Ray Diagrams

Representation of Images Formed by Spherical Mirrors Using Ray Diagrams:

Many rays of light are coming from the point object or an extended object in all directions.The reflection of light follows the same two rules for all rays. The image of the object is formed at the intersection of the reflected rays To construct a ray diagram in order to locate the image of an object, it is more convenient to consider only two rays. The intersection of at least two reflected rays gives the position of image of the point object.

The following rays can be considered for locating the image

1.The rays coming parallel to the principal axis, pass through the focus after reflection in concave mirror or appear to come from focus in the case of convex mirror.

2. The rays coming through the focus of a concave mirror or coming towards focus of a convex mirror, become parallel to principal axis after reflection from the mirror.

3. A ray coming through centre of curvature of a concave mirror or towards the direction of centre of curvature of a convex mirror, reflects back along the same path on striking the mirror surface.

4. A ray incident obliquely to principal axis towards a pole P of the concave or convex mirror is reflected obliquely , following the laws of reflection. i.e., <i = <r.

Point Object On the Principal Axis:

When the point source is placed at the principal axis of a spherical mirror. The ray along the principal axis will fall normally on the mirror and will retrace its path after reflection. Any other ray which will fall on the mirror will be reflected back (after projection) will cut the principal axis. The image of the point source is formed at that point on the principal axis.

Extended Object Placed Perpendicularly On the Principal Axis:

When the extended object is placed perpendicularly at the principal axis of a spherical mirror, the image of the extended object can be formed by locating the images of the individual point of the object. We can find the whole image by just locating the image of the top and the bottom of the object.

The ray along the principal axis will fall normally on the mirror and will retrace its path after reflection. Any other ray which will fall on the mirror will be reflected back (after projection) will cut the principal axis. The image of the point source is formed at that point on the principal axis.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Which of the following are correct : (a) The rays coming parallel to the principal axis, pass through the focus after reflection in concave mirror. (b) The rays coming through the focus of a concave mirror or coming towards focus of a convex mirror, become parallel to principal axis after reflection from the mirror. (c) A ray coming through centre of curvature of a concave mirror, reflects back along the same path on striking the mirror surface.
A. Only (a) and (b) are correct.		B. Only (b) and (c) are correct.
C. Only (a) and (c) are correct.		D. All of these.
Right Option : D
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Question : 2

Which of the following are correct : (a) Many rays of light are coming from the point object or an extended object in all directions. (b) The image of the object is formed at the intersection of the reflected rays. (c) The intersection of at least two reflected rays gives the position of image of the point object.
A. Only (a) and (b) are correct.		B. Only (b) and (c) are correct.
C. Only (a) and (c) are correct.		D. All of these.
Right Option : D
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Question : 3

The rays coming _________________ to the principal axis, pass through the focus after reflection in concave mirror or appear to come from focus in the case of convex mirror.
A. Parallel	B. Perpendicular	C. Inclined	D. None of these.
Right Option : A
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