JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
When an object is placed 40 cm away from a spherical mirror an image of magnification \(\frac{1}{2}\) is produced. To obtain an image with magnification of \(\frac{1}{3}\), the object is to be moved :
- A 40 cm away from the mirror.
- B 80 cm away from the mirror.
- C 20 cm towards the mirror.
- D 20 cm away from the mirror.
Answer & Solution
Correct Answer
(A) 40 cm away from the mirror.
Step-by-step Solution
Detailed explanation
\begin{aligned} & \mathrm{m}=\frac{1}{2}=\frac{\mathrm{f}}{\mathrm{f}-\mathrm{u}} \\ & \frac{1}{2}=\frac{\mathrm{f}}{\mathrm{f}-(-40)} \\ & \mathrm{f}+40=2 \mathrm{f} \Rightarrow \mathrm{f}=40 \mathrm{~cm} \\ & \text { now } \mathrm{m}=\frac{1}{3}=\frac{40}{40-\mathrm{u}} \\ &…
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