Physics
A convex lens of focal length f is divided into two equal parts by a plane parallel to the principal axis. The focal length of each part will be :
- 2f
- f/2
- f
- infinite
Refraction Lens
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Answer
f
Reason — When a convex lens is divided into two equal parts by a plane parallel to its principal axis, each half retains the same curvature of its refracting surfaces as the original lens.
Since the focal length of a lens depends only on the refractive index and the radii of curvature (and not on the aperture or width of the lens), cutting the lens in this manner does not alter these parameters.
Therefore, each half behaves like a complete lens with reduced aperture but unchanged optical power.
Hence, the focal length of each part remains equal to f.
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Related Questions
The radius of the sphere whose part is the lens surface is called the …………… of that surface.
- centre of curvature
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Identify the incorrect statement :
- if the medium on both sides of a lens is same, its first and second focal lengths are equal, i.e. f1 = f2 (numerically).
- when we say focal length of a lens, we mean the first focal length of the lens.
- a convex lens has a real focus.
- a concave lens has a virtual focus.
What is a lens?
Which lens is converging —
(i) an equiconcave lens or an equiconvex lens?
(ii) a concavo-convex lens or a convexo-concave lens?