Question:
An object placed at $10$ cm in front of a concave mirror of focal length $8$ cm gives image of magnification of
An object placed at $10$ cm in front of a concave mirror of focal length $8$ cm gives image of magnification of
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For mirrors:
- Always use sign convention carefully
- Magnification sign indicates nature, magnitude gives size
Updated On: Apr 30, 2026
- $4$
- $6$
- $8$
- $2$
- $10$
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The Correct Option is A
Solution and Explanation
Concept:
Mirror formula:
\[
\frac{1}{f} = \frac{1}{v} + \frac{1}{u}
\]
Magnification:
\[
m = -\frac{v}{u}
\]
Step 1: Use sign convention.
\[ u = -10\ \text{cm}, \quad f = -8\ \text{cm} \]
Step 2: Apply mirror formula.
\[ \frac{1}{-8} = \frac{1}{v} + \frac{1}{-10} \] \[ \frac{1}{v} = -\frac{1}{8} + \frac{1}{10} = \frac{-5 + 4}{40} = -\frac{1}{40} \] \[ v = -40\ \text{cm} \]
Step 3: Find magnification.
\[ m = -\frac{v}{u} = -\frac{-40}{-10} = -4 \]
Step 4: Final answer.
\[ |m| = 4 \]
Step 1: Use sign convention.
\[ u = -10\ \text{cm}, \quad f = -8\ \text{cm} \]
Step 2: Apply mirror formula.
\[ \frac{1}{-8} = \frac{1}{v} + \frac{1}{-10} \] \[ \frac{1}{v} = -\frac{1}{8} + \frac{1}{10} = \frac{-5 + 4}{40} = -\frac{1}{40} \] \[ v = -40\ \text{cm} \]
Step 3: Find magnification.
\[ m = -\frac{v}{u} = -\frac{-40}{-10} = -4 \]
Step 4: Final answer.
\[ |m| = 4 \]
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