Assertion `:` Spherical aberration occur in lenses of larger aperture.
Reason `:` The two rays, paraxial and marginal rays focus at different points.

Write the difference between paraxial rays and marginal rays.

Assertion :- Chromatic aberration occur in simple lenses but not in mirrors. Reason :- Focal length varies with wavelength in case of lenses and not in mirrors.

Assertion : X - rays travel with the speed of light. Reason : X - rays are electromagnetic rays.

Assertion : X - rays cannot be diffracted by means of grating . Reason : X - rays does not obey Bragg's law.

With the help of ray diagram explain what do marginal and paraxial rays mean.

Rays parallel to principal axis, incident on the spherical mirror at different heights from principal axis are focused at different points. And due to this reason we cannot define unique focus. This is known as spherical aberration. Angle of incidence theta shown in figure depends on the height of ray above principal axis. Focal length of spherical mirror can be easily written in terms of angle theta shown in figure as follows : f = R- (R)/(2)sec theta Here R is radius of curvature of mirror. The light rays which are very close to principal axis are known as paraxial rays and rays far away from principal axis are called marginal rays. Let f_(P) and fm represent the focal length corresponding to paraxial rays and marginal rays respectively then

A : Lenses of large aperture suffer from spherical aberration. R : The curvature of the lens at central and peripheral regions is different.

Rays parallel to principal axis, incident on the spherical mirror at different heights from principal axis are focused at different points. And due to this reason we cannot define unique focus. This is known as spherical aberration. Angle of incidence theta shown in figure depends on the height of ray above principal axis. Focal length of spherical mirror can be easily written in terms of angle theta shown in figure as follows : f = R- (R)/(2)sec theta Here R is radius of curvature of mirror. The light rays which are very close to principal axis are known as paraxial rays and rays far away from principal axis are called marginal rays. For paraxial rays focal length is approximately

Rays parallel to principal axis, incident on the spherical mirror at different heights from principal axis are focused at different points. And due to this reason we cannot define unique focus. This is known as spherical aberration. Angle of incidence theta shown in figure depends on the height of ray above principal axis. Focal length of spherical mirror can be easily written in terms of angle theta shown in figure as follows : f = R- (R)/(2)sec theta Here R is radius of curvature of mirror. The light rays which are very close to principal axis are known as paraxial rays and rays far away from principal axis are called marginal rays. What will be the focal length for ray which is incident at an angle 60^(@) ?