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Reflection of Light — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceReflection of Light3 Marks
Question
A mirror forms an image which is 30cm from an object and twice its height.
  1. Where must the mirror be situated?
  2. What is the radius of curvature?
  3. Is the mirror convex or concave?
✓

Answer

Let the image formed is virtual and erect.v - u = 30cm
m = 2
  1. $\text{m}=-\frac{\text{v}}{\text{u}}$
$2=-\frac{\text{v}}{\text{u}}$
$\Rightarrow{\text{v}}=2{\text{u}}$
$2\text{u}-\text{u}=30\text{cm}$
$\text{u}=-10\text{cm}$
  1. $\text{v}=-2\text{u}=20\text{cm}$
$\frac{1}{\text{v}}+\frac{1}{\text{u}}=\frac{1}{\text{f}}$
$\frac{1}{\text{f}}=\frac{-1}{20}$
$\text{f}=-20\text{cm}$
$\text{R}=2\text{f}=-40\text{cm}$
  1. Concave mirror.

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