JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
A mirror is used to produce an image with magnification of \(\frac{1}{4}\). If the distance between object and its image is 40 cm , then the focal length of the mirror is ________
- A 10 cm
- B 12.7 cm
- C 10.7 cm
- D 15 cm
Answer & Solution
Correct Answer
(C) 10.7 cm
Step-by-step Solution
Detailed explanation
\begin{aligned} & \mathrm{m}=-\frac{\mathrm{v}}{\mathrm{u}}=-\left(\frac{\mathrm{v}}{-\mathrm{u}}\right)=\frac{\mathrm{v}}{\mathrm{u}} \\ & \frac{1}{4}=\frac{\mathrm{v}}{\mathrm{u}} \Rightarrow \mathrm{u}=4 \mathrm{v} \\ & \mathrm{v}+\mathrm{u}=40 \\ & 5 \mathrm{v}=40 \\ &…
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