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  • Shown in the figure is a bi-convex lens made of different transparent strips of two different refractive indexes. If the parallel rays of light is incident on the lens; <img alt="" src="http

Shown in the figure is a bi-convex lens made of different transparent strips of two different refractive indexes. If the parallel rays of light is incident on the lens;

 

Option: 1

rays will intersect before focussing


Option: 2

rays will be focussed at two different points


Option: 3

the lens may have four focal points different from each other.


Option: 4

All of the these


Answers (1)

best_answer


Shown in the ray diagram, is an incident beam of parallel rays 1,2,3 & 4. Rays 1 & 3 pass through the medium 1
\Rightarrow It has a focal length \mathrm{f}_{1} given as

\mathrm{f}_{1}=\frac{\mathrm{R}_{1}}{2\left(\mathrm{n}_{1}-1\right)}

Similarly rays 2 and 4 pass through the medium 2.
\Rightarrow It has a focal length

\mathrm{f_{2}=\frac{R_{1}}{2\left(n_{2}-1\right)}}
when \mathrm{n_{2}>n_{1}, f_{2}<f_{1}} and vice versa.

Therefore there are two focal points at right hand sides; for the other sides \mathrm{f}_{1}^{\prime}=\frac{\mathrm{R}_{2}}{2\left(\mathrm{n}_{1}-1\right)}$ and $\mathrm{f}_{2}^{\prime}=\frac{\mathrm{R}_{1}}{2\left(\mathrm{n}_{2}-1\right)}. Therefore another two focal points are for left hand side. We see that the focal points (focal lengths) need not to be same if \mathrm{R_{1} \neq R_{2}} we obtain four focal points but they are different from each other

\mathrm{\therefore \mathrm{D}}

 

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vinayak

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