light-reflection and refraction — Science STD 10 — Question
Gujarat BoardEnglish MediumSTD 10Sciencelight-reflection and refraction2 Marks
Question
Explain the terms for a convex lens : Principal focus
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Answer
When the rays parallel to the principal axis of a convex lens are refracted through the lens, they converge at a point on the principal axis. This point is called the principal focus $F$ of the convex lens.
When the rays parallel to the principal axis of a concave lens are refracted through the lens, they appear to diverge from a point on the principal axis.
This point is called the principal focus F of the concave lens.
A lens has two principal foci $F_1$ and $F_2$ on either side of the lens.
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