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Science · 2024 · 4 marks
CBSE 2024 · Region 1 · Set 1 · Q39
Study the data given below showing the focal length of three concave mirrors A, B and C and the respective distances of objects placed in front of…
Study the data given below showing the focal length of three concave mirrors $\displaystyle \mathrm{A}, \mathrm{B}$ and C and the respective distances of objects placed in front of the mirrors :
| Case | Mirror | Focal Length (cm) | Object Distance (cm) |
| $\displaystyle 1$ | A | $\displaystyle 20$ | $\displaystyle 45$ |
| $\displaystyle 2$ | B | $\displaystyle 15$ | $\displaystyle 30$ |
| $\displaystyle 3$ | C | $\displaystyle 30$ | $\displaystyle 20$ |
(i)
In which one of the above cases the mirror will form a diminished image of the object ? Justify your answer.
(ii)
List two properties of the image formed in case 2.
(iii)
(A)
What is the nature and size of the image formed by mirror C ? Draw ray diagram to justify your answer.
OR
(B)
An object is placed at a distance of $\displaystyle 18$ cm from the pole of a concave mirror of focal length $\displaystyle 12$ cm. Find the position of the image formed in this case.
Marking-scheme solution
(i)
Mirror A.
as the object is placed beyond the centre of curvature of the mirror.
(ii)
Same size/ Real / Inverted
(iii)
Nature-Virtual and erect Size-magnified
Here $\displaystyle f=-12 \mathrm{~cm}, u=-18 \mathrm{~cm}, v=$ ?
Mirror formula $\displaystyle \frac{1}{f}=\frac{1}{v}+\frac{1}{u} \quad$ or $\displaystyle \frac{1}{v}=\frac{1}{f}-\frac{1}{u}$
\[\frac{1}{v}=\frac{1}{-12}-\frac{1}{-18}
\]
\[\mathrm{v}=-36 \mathrm{~cm}
\]
In front of the mirror at a distance of $\displaystyle 36$ cm from the pole of the mirror.
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CBSE Class 10 Science past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.