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Science Answer the questions.[Phy-5M]

MODEL PAPER - 9 [2026] · CBSE STD 10 (CBSE - English Medium). 2 questions.

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Answer the questions.[Phy-5M]

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Question 15 Marks
i. A concave mirror of focal length 10 cm can produce a magnified real as well as virtual image of an object placed in front of it. Draw ray diagrams to justify this statement.
ii. An object is placed perpendicular to the principal axis of a convex mirror of focal length 10 cm . The distance of the object from the pole of the mirror is 10 cm . Find the position of the image formed.
Answer
a. A concave mirror of focal length $f=10 \mathrm{~cm}$ can produce a magnified real image if an object is placed between $F$ and $C$ (i.e.,when $20 \mathrm{~cm}>\mathrm{u}>10 \mathrm{~cm}$ ) as shown in Fig. (a). However, the same mirror may form a magnified virtual image when object is placed between P and F (i.e., $\mathrm{u}<10 \mathrm{~cm}$ ) as shown in Fig. (b).
Image
b. Here focal length of convex mirror $\mathrm{f}=+10 \mathrm{~cm}$, distance of the object from the pole $\mathrm{u}=-10 \mathrm{~cm}$ As per formula,
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$, wehave
$\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{+10}-\frac{1}{-10}$
$=\frac{1}{10}+\frac{1}{10}=\frac{1}{5}$
$\Rightarrow \mathrm{v}=+5 \mathrm{~cm}$
Thus, image is formed behind the mirror at 5 cm from the pole of mirror.
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Question 25 Marks
a. List four characteristics of the image formed by a concave lens of focal length 20 cm when the object is placed at a distance of 40 cm from its optical centre.
b. The size of image of an object by a convex lens of focal length 20 cm is observed to be reduced to $\frac{1}{3} \mathrm{rd}$ of its size. Find the distance of the object from the optical centre of the lens.
Answer
i. • Virtual
• Erect
• Diminished
• On the same side of the object
ii. Focal Length $=20 \mathrm{~cm}$.
u = -x cm
$\mathrm{v}=\frac{\mathrm{x}}{3}$
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\mathrm{x}=80 \mathrm{~cm}$
Hence, the distance of the object from the optical centre of the lens is 80 cm .
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