Define the principal focus of a concave mirror.

The point on the principal axis of a concave mirror where the rays of light coming from infinity or parallel to the principal axis meet after reflection from the mirror is called the principal focus of a concave mirror.

• It is denoted by the symbol F.
• The principal focus is also referred to as simply focus or focal point.
• The principal focus of a concave mirror lies in front of the mirror.
• The distance between the pole and the principal focus of the concave mirror is called the focal length.
• A line passing through the principal focus and perpendicular to the principal axis on which the rays of light coming from a distant object making different angles with the principal axis converge or diverge is known as a focal plane.
• A concave mirror is also known as a convergent mirror.

Location of principal focus of the concave mirror

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