The focal point, also known as the focus, is the point on the principal axis where parallel rays of light converge or appear to diverge from after passing through a lens or reflecting off a mirror.
Imagine you are standing in front of a magnifying glass and focusing sunlight onto a piece of paper. The spot where all the sunlight converges and becomes intense is like the focal point.
Converging Lens: A lens that brings parallel rays of light together at its focal point.
Diverging Lens: A lens that causes parallel rays of light to spread out as if they came from its focal point.
Principal Axis: An imaginary line passing through the center of curvature, vertex, and focal points of a lens or mirror.
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