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Question
Which of the following (referred to a spherical mirror) do (does) not depend on whether the rays are paraxial or not?
Which of the following (referred to a spherical mirror) do (does) not depend on whether the rays are paraxial or not?
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Solution
The correct option is D Principal axis.
According to the Paraxial Approximation, rays parallel to the principal axis can be focused at one point after reflection, only if they are close to the principal axis. What if parallel rays are incident on a spherical mirror which are not close to the principal axis ? In this case, the reflected rays will not intersect the principle axis at one single point but at different points. Hence, there is no concept of focus. We can now say that the definition of focus depends on the rays being paraxial.
Also, Pole is the mid-point of the surface of the mirror, whether the rays are paraxial or not, the mid−point of the mirror doesn't change. Radius of curvature is the radius of the sphere, the mirror is part of, even this definition is independent of whether the rays are close to principal axis or not. Principal axis is the line joining the pole to the center of curvature, if light rays are not close to the principal axis, pole and center of curvature doesn’t change, hence neither does the definition of principal axis. So, we conclude that only the definition of focus changes.
According to the Paraxial Approximation, rays parallel to the principal axis can be focused at one point after reflection, only if they are close to the principal axis. What if parallel rays are incident on a spherical mirror which are not close to the principal axis ? In this case, the reflected rays will not intersect the principle axis at one single point but at different points. Hence, there is no concept of focus. We can now say that the definition of focus depends on the rays being paraxial.
Also, Pole is the mid-point of the surface of the mirror, whether the rays are paraxial or not, the mid−point of the mirror doesn't change. Radius of curvature is the radius of the sphere, the mirror is part of, even this definition is independent of whether the rays are close to principal axis or not. Principal axis is the line joining the pole to the center of curvature, if light rays are not close to the principal axis, pole and center of curvature doesn’t change, hence neither does the definition of principal axis. So, we conclude that only the definition of focus changes.
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