Advertisements
Advertisements
प्रश्न
State how the focal length of a glass lens (Refractive Index 1.5) changes when it is completely immersed in:
(i) Water (Refractive Index 1.33)
(ii) A liquid (Refractive Index 1.65)
उत्तर
We know
`1/"f" = (mu - 1) (1/"R"_1 - 1/"R"_2)`
When the lens is submerged into water of R.I. = 1.33, then `1/"f" = (mu_12 - 1) (1/"R"_1 - 1/"R"_2)`
`("f"')/"f" = (mu -1)/(mu_12 - 1) = ((1.56 - 1)/(1.56/1.33 -1))`
`therefore ("f"')/"f" = ((0.56) xx 1.33)/(1.56 - 1.33) = 3.24`
Thus, focal length of the lens increases.
Similarly, for another liquid
`("f"')/"f" = ((1.56 - 1)/(1.56/1.65 - 1)) = - (0.56 xx 1.65)/0.09 = - 9.7`
i.e. the convex lens behaves as a concave lens.
APPEARS IN
संबंधित प्रश्न
In motor vehicles, a convex mirror is attached near the driver's seat to give him the view of the traffic behind. What is the special function of this convex mirror which a plane mirror can not do?
Following figure shows three transparent media of refractive indices \[\mu_1 , \mu_2 \text{ and } \mu_3\]. A point object O is placed in the medium \[\mu_2\]. If the entire medium on the right of the spherical surface has refractive index \[\mu_3\], the image forms at O". In the situation shown,
Light is incident from glass (μ = 1.5) to air. Sketch the variation of the angle of deviation δ with the angle of incident i for 0 < i < 90°.
A spherical surface of radius 30 cm separates two transparent media A and B with refractive indices 1.33 and 1.48 respectively. The medium A is on the convex side of the surface. Where should a point object be placed in medium A so that the paraxial rays become parallel after refraction at the surface?
A narrow pencil of parallel light is incident normally on a solid transparent sphere of radius r. What should be the refractive index is the pencil is to be focussed (a) at the surface of the sphere, (b) at the centre of the sphere.
How can the spherical aberration produced by a lens be minimized?
Two thin lenses having optical powers of -10D and+ 6D are placed in contact with each other. The focal length of the combination is:
According to Cartesian sign convention, all distances are measured from the _______.
Focal length of a mirror is given by ______.
A short object of length L is placed along the principal axis of a concave mirror away from focus. The object distance is u. If the mirror has a focal length f, what will be the length of the image? You may take L << |v – f|.
