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Light – Reflection and Refraction — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceLight – Reflection and Refraction1 Mark
MCQ
A student focussed the Sun rays using an optical device $'X\ ’$ on a screen $S$ as shown. From this it may be concluded that the device $'X\ ’ $ is a $($select the correct option$)$
  • A
    Convex lens of focal length $10\ cm.$
  • B
    Convex lens of radius of curvature $20\ cm.$
  • ✓
    Convex lens of focal length $20\ cm.$
  • D
    Concave mirror of focal length $20\ cm.$
✓

Answer

Correct option: C.
Convex lens of focal length $20\ cm.$
Light rays from infinity are converged at the focal point of the convex lens. Therefore, the focal length of the convex lens is $20\ cm.$
Hence, the correct option is $C$.

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