Page 1 - Lesson note reflection through concave mirror

SAI INTERNATIONAL SCHOOL

PHYSICS

CLASS X

Chapter:LIGHT-REFLECTION AND REFRACTION

MODULE-23

Concave Mirror Image formation

Rays emerging from a point meet at another point after reflection, and that point is
called the image of the first point. The image is real if the rays converge to the point

and it is virtual if the rays do not meet it but appear to diverge from a point when the

rays are produced backwards. During image formation we assume that the rays are
paraxial, i.e., they are incident at points close to the pole P of the mirror and make

small angles with the principal axis. For a concave mirror, we consider six positions
of the object before the mirror.

Different positions of object

1. When the object is placed at infinity,

2. When the object is placed beyond C (centre of curvature)

3. When the object is placed at C

4. When the object is placed between C and F (principal focus)

5. When the object is placed at F

6. When the object is placed between F and P (Pole)

When the Object is at Infinity

In this condition, we consider two rays parallel to the principal axis originating from
the object. These rays after reflection converge and form an image at F, the principal

focus of the mirror, in front of the mirror. The image thus formed is highly diminished,

point size, real and inverted.

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