Define the principal focus of convex and concave mirrors. Define focal length. Which mirror has a positive focal length? Which has a negative focal length and why?

Principal focus: The point where parallel rays meet or appear to diverge after reflection.

Focal length (f): The distance between the pole (P) and focus (F).

Positive focal length: A convex mirror has a positive focal length because its focus is behind the mirror.

Negative focal length: A concave mirror has a negative focal length because its focus is in front of the mirror.

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