Ray Optics and Optical Instruments — Physics STD 12 Science — Question
Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
Question
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Answer
If the far point goes ahead, the power of the divergent lens should be reduced.
If the far point is 1m away from the eye, the divergent lens should be used.
Explanation:
As the far point (x) is shifited ahead, the focal length (f) will be increased.
thus. we have
$\frac{1}{\text{f}}=\frac{1}{\text{v}}-\frac{1}{\text{u}}$
$\Rightarrow \frac{1}{\text{f}}=\frac{1}{-\text{x}}-\frac{1}{-\infty}$
$\Rightarrow \frac{1}{\text{f}}=\frac{1}{-\text{x}}$
$\Rightarrow\text{f}=-\text{x}$
As power (p) is equal to reciprocal of the focal length, it will be reduced, Also, because the focal length is negative, the lens used will be divergent when the far point is 1m away.
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