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Lens Maker's Formula - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main
Quick Facts
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Lens Maker's formula is considered one the most difficult concept.
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33 Questions around this concept.
Solve by difficulty
A thin convex lens made from crown glass has a focal length of f. When it is measured in two different liquids having refractive indices
and
it has the focal lengths
respectively. The correct relation between the focal lengths is :
A convex lens, of focal length 30 cm, a concave lens of focal length 120 cm, and a plane mirror are arranged as shown. For an object kept at a distance of 60 cm from the convex lens, the final image, formed by the combination, is a real image, at a distance of :
To find the focal length of a convex mirror, a student records the following data :
|
Object Pin |
Convex Lens | Convex Mirror |
Image Pin |
| 22.2 cm | 32.2 cm | 45.8 cm | 71.2 cm |
The focal length of the convex lens is 1 and that of mirror is
2. Then taking index correction to be negligibly small,
1 and
2 are close to :
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Diameter of a plano - convex lens is 6 cm and thickness at the centre is 3 mm. If speed of the light in material of lens is 2 x 108 m/s, the focal length of the lens is :
An object 2.4 m in front of a lens forms a sharp image on a film 12 cm behind the lens. A glass plate 1cm thick, of refractive index 1.50 is interposed between lens and film with its plane faces parallel to film. At what distance (from lens) should object be shifted to be in sharp focus on film?
A double convex thin lens made out of glass (refractive index, ) has both radii of curvature of magnitude
. Incident light rays parallel to the axis of the lens will converge at a distance
such that:
The focal length of the lens of refractive index in air is
. If air is replaced by water of
, its focal length is:
Concepts Covered - 1
Lens Maker's formula
Lens Maker's formula -
Derivation of Lens maker formula -
Let us take a lens having refractive index = and the surrounding is having refractive index =
. Also, let us assume that the lens is having two refracting surfaces having radii R1 and R2.
Here I' is the intermediate image and I is the final image.
As we have learned the formula of refraction at a single spherical surface. Let us apply this to the surface ACB, we get -
Similarly for the second surface ADB-
Here, v1 is the position of the image formed by the first surface and the same image will now act as an object for the second surface.
Now adding equations (1) and (2),
Now we are going to arrange this equation in the desired as -
we get,
Where,
There are certain limitations of this lens maker’s formula -
- The lens should not be thick so that the space between the two refracting surfaces can be small.
- The medium used on both sides of the lens should always be the same.
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