EASY

Earn 100

Explain the paraxial rays?

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 rods

S_{1}

and

S_{2}

(refractive index = 1.5) have one convex end of radius of curvature 10 cm. They are placed with the curved surfaces at a distance d as shown in the figure, with their axes (shown by the dashed line) aligned. When a point source of light

P

is placed inside rod

S_{1}

on its axis at a distance of 50 cm from the curved face, the light rays emanating from it are found to be parallel to the axis inside

S_{2}

. The distance

d

HARD

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

A thin convex lens of focal length

f

is put on a plane mirror as shown in the figure. When an object is kept at a distance

a

from the lens-mirror combination, its image is formed at a distance

\frac{a}{3}

in front of the combination. The value of

a

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

A thin convex lens

L

(refractive index

= 1.5

) is placed on a plane mirror

M

. When a pin is placed at

A

, such that

O A = 18 c m,

its real inverted image is formed at

A

itself, as shown in figure. When liquid of refractive index

μ_{l}

is put between the lens and the mirror, the pin has to be moved to

A^{'},

such that

O A^{'} = 27 c m,

to get its inverted real image at

A'

itself. The value of

μ_{l}

will be

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

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 glycerin (which has the same refractive index (

μ = 1.5

) as that of glass), then the equivalent focal length is

F_{2} .

The ratio

F_{1} : F_{2}

will be

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

A convex lens of focal length

25 cm

produces images of the same magnification

2

, when an object is kept at two positions

x_{1}

and

x_{2}

(x_{1} > x_{2})

from the lens. The ratio of

x_{2}

and

x_{1}

HARD

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

Sunlight of intensity

1 .3 kW m^{- 2}

is incident normally on a thin convex lens of focal length

20 cm

. Ignore the energy loss of light due to the lens and assume that the lens aperture size is much smaller than its focal length. The average intensity of light, in

kW m^{- 2}

, at a distance

22 cm

from the lens on the other side is __________.

MEDIUM

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

Diameter of a plano - convex lens is

6 cm

and thickness at the centre is

3 mm

. If the speed of light in the material of lens is

2 \times 1 0^{8} m s^{- 1}

, the focal length of the lens is:

MEDIUM

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

A light ray enters a solid glass sphere of refractive index $μ = \sqrt{3}$ at an angle of incidence $60 °$ . The ray is both reflected and refracted at the farther surface of the sphere. The angle (in degrees) between the reflected and refracted rays at this surface is:

HARD

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

The eye can be regarded as a single refracting surface. The radius of curvature of this surface is equal to that of the cornea

(7 .8 mm)

. This surface separates two media of refractive indices

1

and

1.34

. Calculate the distance from the refracting surface at which a parallel beam of light will come to focus.

MEDIUM

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

A parallel beam of light strikes a piece of transparent glass having cross section as shown in the figure below. Correct shape of the emergent wavefront will be (figures are schematic and not drawn to scale)

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HARD

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

A transparent thin film of uniform thickness and refractive index $n_{1} = 1.4$ is coated on the convex spherical surface of radius R at one end of a long solid glass cylinder of refractive index $n_{2} = 1.5$ , as shown in the figure. Rays of light parallel to the axis of the cylinder traversing through the film from air to glass get focused at distance f₁ from the film, while rays of light traversing from glass to air get focused at distance f₂ from the film. Then

Question Image

HARD

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

A beaker of radius $r$ is filled with water $(refractive index \frac{4}{3})$ up to a height $H$ as shown in the figure on the left. The beaker is kept on a horizontal table rotating with angular speed $ω$ . This makes the water surface curved so that the difference in the height of water level at the centre and at the circumference of the beaker is $h (h ≪ H, h ≪ r)$ , as shown in the figure on the right. Take this surface to be approximately spherical with a radius of curvature $R .$ Which of the following is/are correct? ( $g$ is the acceleration due to gravity)

Question Image

HARD

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

A converging mirror is placed on the right hand side of a converging lens as shown in the figure. The focal length of the mirror and the lens are $20 cm$ and $15 cm$ respectively. The separation between the lens and the mirror is $40 cm$ and their principal axes coincide. A point source is placed on the principal axis at a distance $d$ to the left of the lens. If the final beam comes out parallel to the principal axis, then the value of $d$ is:

Question Image

MEDIUM

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

A convex lens is in contact with a concave lens. The magnitude of the ratio of their focal length is

\frac{5}{3} .

If their equivalent focal length is

45 cm,

the individual focal lengths of concave and convex lens are respectively.

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

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?

HARD

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

A plano-convex lens is made of a material of refractive index n. When a small object is placed 30 cm away in front of the curved surface of the lens, an image of double the size of the object is produced. Due to reflection from the convex surface of the lens, another faint image is observed at a distance of 10 cm away from the lens. Which of the following statement(s) is (are) true?

Explain the paraxial rays?

Important Questions on Ray Optics and Optical Instruments

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