0
You visited us 0 times! Enjoying our articles? Unlock Full Access!
Question

# Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of the combination is $$F_1$$. When the space between the two lenses is filled with glycerine (which has the same refractive index ($$\mu = 1.5$$) as that of glass) then the equivalent focal length is $$F_2$$. The ratio $$F_1 : F_2$$ will be :

A
$$1 : 2$$
B
$$2 : 1$$
C
$$2 : 3$$
D
$$3 : 4$$
Solution
Verified by Toppr

#### Correct option is B. $$1 : 2$$Equivalent focal length in air,$$\dfrac{1}{F_1} = \dfrac{1}{f} + \dfrac{1}{f} = \dfrac{2}{f}$$ When glycerin is filled inside, glycerin lens behaves like a diverging lens of focal length (-f)$$\implies \dfrac{1}{F_2} = \dfrac{1}{f} + \dfrac{1}{f} - \dfrac{1}{f}$$$$= \dfrac{1}{f}$$$$\implies \dfrac{F_1}{F_2} = \dfrac{1}{2}$$

57
Similar Questions
Q1
Two similar thin equiconvex lenses of focal length f each are kept coaxially in contact with each other such that the focal length of the combination is F1. When the space between the two lenses is filled with glycerin (which has the same refractive index (μ=1.5) as that of lens, the equivalent focal length is F2. The ratio F1 : F2 will be
View Solution
Q2
Two similar thin equi convex lenses of focal length f each are kept coaxiallyin contact with each other such that the focal length of the combination is F1 when the space between the two lenses is filled with glycerine (which has the same refractive index (μ=1.5) as that of glass ) then the equivalent focal length is F2 the rati
View Solution
Q3
2 thin convex lenses, each of focal length f are placed in contact coaxially. The focal length of combination is F1. When the space between the surface of the lenses are filled with the same material of which the lens are made, the equivalent focal length becomes F2. What is the ratio of F1 and F2?
View Solution
Q4
When two thin lenses of focal lengths f1 and f2 are kept coaxially and in contact, prove that their combined focal length "f" is given by
1f=1f1+1f2
View Solution
Q5
If two thin lenses of focal length f1 and f2 are kept in contact to each other, then the equivalent focal length of the combination
View Solution