Question

Two convex lens are made up of glass are placed in a cclosd contact with each other. If focal length of both lens is f. If space between them is filled with same material then effective focal length is

Answer 1

Answer:

The effective focal length of the system is f

Explanation:

If the focal length of two convex lenses is f_1f1 and f_2f2 and they are in close contact with each other

Then the effective focal length of the system is given by

\frac{1}{F}=\frac{1}{f_1}+\frac{1}{f_2}F1=f11+f21

However, if third material is added in between such that it acts as concave lens with focal length f_3f3

Then, the effective focal length is given by

\frac{1}{F}=\frac{1}{f_1}+\frac{1}{f_2}-\frac{1}{f_3}F1=f11+f21−f31

Here, given that

Two lenses that are in close contact have focal length ff

And, the space between them is filled by same glass material

Since the refractive index is same and the radius of curvature of the lens is also same

Therefore, this diverging lens will also have focal length ff

Therefore,

The effective focal length

\frac{1}{F}=\frac{1}{f}+\frac{1}{f}-\frac{1}{f}F1=f1+f1−f1

\implies \frac{1}{F}=\frac{1}{f}⟹F1=f1

\implies F=f⟹F=f

Therefore, the effective focal length of the system is f

Hope this answer is helpful.

Know More:

Q: An optical system uses two thin convex lenses in contact having the effective focal length of 30/4cm If one lens has focal length of 30cm. find the focal length of the other lens.

Explanation:

I hope it is helpful for

Answer 2

Explanation:

answer for you by the sherin