Question

1. Define the following: (a) Principal axis,
(b) Focal length, (c) Pole (d) Centre of curvature.
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Answer 1

Answer:

1. Optical axis, the straight line passing through the geometrical centre of a lens and joining the two centres of curvature of its surfaces. Sometimes the optical axis of a lens is called its principal axis. The path of a light ray along this axis is perpendicular to the surfaces and, as such, will be unchanged.

2. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light.

3.The point where the principal axis pierces the mirror is called the pole of the mirror. ... Rays of light parallel to the principal axis of a concave mirror will appear to converge on a point in front of the mirror somewhere between the mirror's pole and its center of curvature.

4.the center of the circle whose center lies on the concave side of a curve on the normal to a given point of the curve and whose radius is equal to the radius of curvature at that point.