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Ray Optics — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsRay Optics1 Mark
Question
Assertion : The mirrors used in search lights are parabolic and not concave spherical.
Reason : In a concave spherical mirror the image formed is always virtual.
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Answer

(c) In search lights, we need an intense parallel beam of light. If a source is placed at the focus of a concave spherical mirror, only paraxial rays are rendered parallel. Due to large aperture of mirror, marginal rays give a divergent beam.But in case of parabolic mirror, when source is at the focus, beam of light produced over the entire cross-section of the mirror is a parallel beam.

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