Class 12 Physics Ray Optics Optical Instruments - Image Formation By Spherical Mirror

Class 12 Physics Ray Optics Optical Instruments - Image Formation By Spherical Mirror Hand written Notes for board exam

• The rays of light through centre of curvature retrace its path.
• The ray of light parallel to the principal axis, on reflection, passes through the focus.
• The ray of light through F is reflected parallel to the principal axis.
• There are 2 ways an image is formed: -
  • Real image of an object where reflected rays actually meet, they are inverted and formed on the same side of the object.
  • Virtual image of an object where reflected rays appear to meet. They are always erect and cannot be projected on the screen.
  • They are formed beyond the mirror

Sign Convections:-

Following are the sign convections which are to be followed:

1. The pole (P) of the mirror is taken as the origin. The principal axis of the mirror is taken as the x-axis (X’X) of the coordinate system.

(2) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.

(3) All distances parallel to the principal axis are measured from the pole of the mirror.

(4) All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along – x-axis) are taken as negative.

(5) Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive whereas which are measured along (-y axis) are taken as negative.

(vi) The heights measured upwards with respect to x-axis and normal to the principal axis (x-axis) of the mirror/ lens is taken as positive. The heights measured downwards are taken as negative.

(vii) The radius of curvature and the focal length of a concave mirror are negative and those for a convex are positive.

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