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Spherical aberration in spherical mirrors is a defect which is due to dependence of focal length ‘f’ on angle of incidence ‘ q ’ as shown in figure is given by where R is radius of curvature of mirror and q is the angle of incidence The rays which are closed to principal axis are called paraxial rays and the rays far away from principal axis are called marginal rays As a result of above dependence different rays are brought to focus at different points and the image of a point object is on a point If fp and fm represent the focal length of paraxial and marginal rays respectively, then correct relationship is :
- fp = fm
- fp > fm
- fp < fm
- none of these
The correct answer is: fp > fm
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