Define the following terms with respect to spherical mirrors:
(i) Pole
(ii) Centre of curvature
(iii) Principal axis
(iv) Principal focus
Pole:
The middle point of the reflecting surface of a spherical mirror is called a pole. The letter P represents a pole.
Centre of curvature:
It is the centre of the sphere of a glass of which the mirror is a part. The letter C represents the centre of curvature.
Principal axis:
The principal axis of a spherical mirror is the straight line joining the centre of curvature and pole of the mirror.
Principal focus:
The mid-point of CP is called focus (F). It is the point on the principal axis of a spherical mirror where all incident rays parallel to the principal axis meet after reflection.
These points have been represented in the given diagrams.
Concave Mirror:
![](/assets/questions/media/145526-31039-1603172798.png)
Convex Mirror:
![](/assets/questions/media/145526-31039-1603172814.png)
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- (a) Explain with the help of a diagram, why the convex lens is also called a converging lens.(b) Define principal axis, principal focus and focal length of a convex lens.
- In order to obtain a magnification of −2 (minus 2) with a concave mirror, the object should be placed:(a) between pole and focus (b) between focus and centre of curvature(c) at the centre of curvature (d) beyond the centre of curvature
- What happens after refraction, when :(i) a ray of light parallel to the principal axis passes through a concave lens?(ii) a ray of light falls on a convex lens while passing through its principal focus?(iii) a ray of light passes through the optical centre of a convex lens?
- A concave mirror produces magnification of +4. The object is placed:(a) at the focus (b) between focus and centre of curvature(c) between focus and pole (d) beyond the centre of curvature
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