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Standard XII

Physics

Refraction at a Spherical Surface

A concave sph...

Question

A concave spherical refractive surface with radius $R$ separates a medium of refractive index $5 / 2$ from air. As an object is approaching the surface from far away from the surface along the central axis, its image

Always remains real

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Always remains virtual

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Changes from real to virtual when it is at a distance

2 R / 3

from the surface

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Changes from virtual to real when it is at a distance

2 R / 3

from the surface

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Solution

The correct option is D Always remains virtual
$\frac{2.5}{v} - \frac{1}{- u} = \frac{1.5}{- R}$
$v = - \frac{2.5 u R}{1.5 u + R}$
$v < 0$ for all values of $u$ , so the image remains virtual.

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A concave spherical refractive surface with radius R separates a medium of refractive index 5/2 from air. As an object is approaching the surface from far away from the surface along the central axis, its image

The correct option is D Always remains virtual2.5v−1−u=1.5−Rv=−2.5uR1.5u+Rv<0 for all values of u, so the image remains virtual.

A concave spherical refractive surface with radius $R$ separates a medium of refractive index $5 / 2$ from air. As an object is approaching the surface from far away from the surface along the central axis, its image

The correct option is D Always remains virtual
$\frac{2.5}{v} - \frac{1}{- u} = \frac{1.5}{- R}$
$v = - \frac{2.5 u R}{1.5 u + R}$
$v < 0$ for all values of $u$ , so the image remains virtual.