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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 10cm.
  • B
    Convex lens of radius of curvature 20cm.
  • C
    Convex lens of focal length 20cm.
  • D
    Concave mirror of focal length 20cm.
✓

Answer

  1. Convex lens of focal length 20cm.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

Light rays from infinity are converged at the focal point of the convex lens. Therefore, the focal length of the convex lens is 20cm.

Hence, the correct option is C.

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