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Question: Define (i) Principal Focus of a Concave Mirror, and (ii) Focal Length of a Concave Mirror. Draw a Diagram to Represent the Action of a Concave Mirror on a Beam of Parallel Light Rays. Mark on this Diagram Principal Axis, Focus F, Centre of Curvature C, Pole P, and Focal Length f of the Concave Mirror.
Answer:
(i) Principal Focus of a Concave Mirror
The principal focus (F) of a concave mirror is the point on its principal axis where light rays parallel to the principal axis converge after reflection. It is a real point located on the same side as the object.
(ii) Focal Length of a Concave Mirror
The focal length (f) of a concave mirror is the distance between the pole (P) and the principal focus (F). It determines how strongly the mirror converges or diverges light. The focal length is related to the radius of curvature (R) by the formula:
where R is the radius of curvature (the distance between the pole and the centre of curvature).
Diagram: Concave Mirror and Parallel Light Rays
Here is a diagram representing how a concave mirror focuses parallel light rays:
{Imagine a concave mirror with parallel light rays converging at the focal point, and labelled components: Pole (P), Focus (F), Centre of Curvature (C), Principal Axis, and Focal Length (f).}
- The concave mirror is also known as a converging mirror because it brings parallel light rays to a single point after reflection.
- The real and inverted images formed by a concave mirror have applications in telescopes, vehicle headlights, and shaving mirrors.
- The distance of the object from the mirror determines the type of image formed (real/virtual, magnified/diminished, inverted/erect).
Common Doubts in Physics
