EASY

Earn 100

An achromatic doublet of focal length 90 cm si to be made of two lens. The material of one of the lenses has 1.5 times the dispersive power of the other. The doublet is converting type. Find the focal length of each lens.

Important Questions on Ray Optics and Optical Instruments

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Two identical glass

(μ_{g} = \frac{3}{2})

equiconvex lenses of focal length,

f

are kept in contact. The space between the two lenses is filled with water

(μ_{w} = \frac{4}{3})

. The focal length of the combination is

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

What is the position and nature of image formed by lens combination shown in figure? (

f_{1}, f_{2}

are focal lengths)

Question Image

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Two thin lenses have a combined power of

+ 9 D .

When they are separated by a distance of

20 cm,

their equivalent power becomes

+ \frac{27}{5} D,

then their individual powers are

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

An optical device is constructed by fixing three identical convex lenses of focal lengths

10 cm

each inside a hollow tube at an equal spacing of

30 cm

each. One end of the device is placed

10 cm

away from a point source. How much does the image shift when the device is moved away from the source by another

10 cm ?

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A small object is placed $50 cm$ to the left of thin convex lens of focal length $30 cm$ . A convex spherical mirror of radius of curvature $100 cm$ is placed to the right of the lens at a distance of $50 cm$ . The mirror is tilted such that the axis of the mirror is at an angle $θ = 30 °$ to the axis of the lens, as shown in the figure. If the origin of the coordinate system is taken to be at the centre of the lens, the coordinates (in $cm$ ) of the point $(x, y)$ at which the image is formed are:

Question Image

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A point source of light is moving at a rate of

2 cm s^{- 1}

towards a thin convex lens of focal length

10 cm

along its optical axis. When the source is

15 cm

away from the lens the image is moving at

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A convex lens of focal length

f

is placed some where in between an object and a screen. The distance between object and screen is

x

. If numerical value of magnification produced by lens is

m

, focal length of lens is

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A point object is placed

20 cm

left of a convex lens of focal length,

f = 5 cm

(see the figure). The lens is made to oscillate with a small amplitude

A

along the horizontal axis. The image of the object will also oscillate along the axis with
Question Image

EASY

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A plano-convex lens of refractive index

μ_{1}

and focal length

f_{1}

is kept in contact with another plano-concave lens of refractive index

μ_{2}

and focal length

f_{2} .

If the radius of curvature of their spherical faces is

R

each and

f_{1} = 2 f_{2},

the

μ_{1}

and

μ_{2}

are related as:

EASY

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

Formation of real image using a biconvex lens is shown below:

Question Image

If the whole set up is immersed in water without disturbing the object and the screen positions, what will one observe on the screen?

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A concave lens made of material of refractive index

1.6

is immersed in a medium of refractive index

2.0 .

The two surfaces of the concave lens have the same radius of curvature

0.2 m .

The lens will behave as a

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A plano-convex lens becomes an optical system of

28 cm

focal length when its plane surface is silvered and illuminated from left to right as shown in fig

- A

If the same lens is instead silvered on the curved surface and illuminated from another side as in fig-

B

, it acts as an optical system of focal length

10 cm

. The refractive index of the material of the lens is:

Question Image

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

The image of an object, formed by a plano - convex lens at a distance of

8 m

behind the lens, is real and is one-third the size of the object. The wavelength of light inside the lens is

\frac{2}{3}

times the wavelength in free space. The radius of the curved surface of the lens is

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A diverging lens with magnitude of focal length

25 cm

is placed at a distance of

15 cm

from a converging lens of magnitude of focal length

20 cm

. A beam of parallel light falls on the diverging lens. The final image formed is:

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

The word KVPY is written on $a$ board and viewed through different lenses such that board is at a distance beyond the focal length of the lens.

Question Image

Ignoring magnification effects, consider the following statements.
$(I)$ First image has been viewed from the planar side of a plano-concave lens and second image from the planar side of a plano-convex lens.
$(II)$ First image has been viewed from the concave side of a plano-concave lens and second image from the convex side of a plano-convex lens.
$(III)$ First image has been viewed from the concave side of a plano-concave lens and second image from the planar side of a plano-convex lens.
$(IV)$ First image has been viewed from the planar side of a plano-concave lens and second image from the convex side of a plano-convexlens.

Which of the above statements are correct?

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

In an experiment a convex lens of focal length

15 cm

is placed coaxially on an optical bench in front of a convex mirror at a distance of

5 cm

from it. It is found that an object and its image coincide, if the object is placed at a distance of

20 cm

from the lens. The focal length of the convex mirror is-

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A hollow lens is made of thin glass and in the shape of a double concave lens. It can be filled with air, water of refractive index 1.33 or

C S_{2}

of refractive index 1.6. It will act a diverging lens if it is

MEDIUM

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A plano - convex lens (focal length

f_{2}

, refractive index

μ_{2},

radius of curvature R) fits exactly into a plano - concave lens (focal length

f_{1},

refractive index

μ_{1},

radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be:

HARD

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

A convex lens is put

10 c m

from a light source and it makes a sharp image on a screen, kept

10 c m

from the lens. Now a glass block (refractive index 1.5) of

1.5 c m

thickness is placed in between the light source and the lens. To get the sharp image again, the screen is shifted by a distance

d .

Then

d

is:

EASY

Physics>Optics>Ray Optics and Optical Instruments>Refraction at Spherical Surfaces and by Lenses

For a thin lens of focal length

f

, if the object and image distances from the optical centre are

u

and

v

, then which of the following is the correct lens formula? (Assume standard sign-convention)

An achromatic doublet of focal length 90 cm si to be made of two lens. The material of one of the lenses has 1.5 times the dispersive power of the other. The doublet is converting type. Find the focal length of each lens.

Important Questions on Ray Optics and Optical Instruments

Learn and Prepare for any exam you want !