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31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2


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31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 1

Focal length of a convex lens of refractive index1.5 is 2 cm. Focal length of the lens whenimmersed in a liquid of refractive index of 1.25 will be [1988]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 1

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 2

Ray optics is valid, when characteristicdimensions are [1989]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 2

Characteristic dimensions must be much
larger than the wavelength of light.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 3

A ray is incident at an angle of incidence i on one surface of a prism of small angle A and emerges normally from the opposite surface. If the refractive index of the material of prism is μ, the angle of incidence i is nearly equal to    [1989]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 3

As refracted ray emerges normally from
oppostite surface, r2 = 0

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 4

A beam of monochromatic light is refracted fromvacuum into a medium of refractive index 1.5,the wavelength of refracted light will be (1991]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 4

Here, c = velocity of light in medium and v =
velocity of light in vacuum;
m = refractive index of the medium.
Hence, wavelength in medium 

(∴ μ > 1, given)

So, the required wavelength decreases.
ALTERNATIVELY,
c =vλ . On refraction, the frequency, v do
not change. When light is refracted from
vacuum to a medium, the velocity, c
decreases. Therefore,  λ also decreases

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 5

Green light of wavelength 5460 Å is incident onan air-glass interface. If the refractive index ofglass is 1.5, the wave length of light in glasswould be (c = 3 × 108 ms–1) [1991]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 5

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 6

There is a prism with refractive index equal to √2 and the refracting angle equal to 30°. One of the refracting surfaces of the prism is polished. A beam of monochromatic light will retrace its path if its angle of incidence over the refracting surface of the prism is [1992]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 6

It is clear from the figure that the ray will
retrace the path when the refracted ray QR is
incident normally on the polished surface AC.
Thus, angle of refraction r = 30°

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 7

Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 3/2 is [1993]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 7

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 8

A point source of light is placed 4 m below thesurface of water of refractive index 5/3. Theminimum diameter of a disc, which should beplaced over the source, on the surface of waterto cut off all light coming out of water is [1994]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 8

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 9

Angle of deviation (δ) by a prism (refractive index = μ and supposing the angle of prism A to be small) can be given by [1994]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 9

When the angle of prism is small, δ = (μ – 1) A

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 10

Focal length of a convex lens will be maximumfor [1994]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 10

For red light, focal length of lens is maximum
because f ∝ λ  and λ is maximum for red
light.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 11

An achromatic combination of lenses is formedby joining [1995]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 11

If two or more lenses are combined together
in such a way that this combination
produces images of different colours at the
same point and of the same size, then this
property is called ‘achromatism’. Concave
and convex type of lenses are used for this
combination.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 12

The hypermetropia is a [1995]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 12

A person suffering from hyper metropia can
see objects beyond a particular point called
the near point. If the object lies at a point
nearer than this point, then image is not
formed at the retina. This is also known as
long-sight defect.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 13

If two mirrors are kept inclined at 60° to eachother and a body is placed at the middle, thentotal number of images formed is [1995]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 13

Angle between two mirrors (θ) = 60º. Number
of images formed by the inclined mirror

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 14

A lens is placed between a source of light and a wall. It forms images of area A1 and A2 on the wall for its two different positions. The area of the source of light is [1995]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 14

Size of images = A1 and A2. From the
displacement method, the area of the source
of light = 

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 15

A convex lens of focal length 80 cm and aconcave lens of focal length 50 cm are combinedtogether. What will be their resulting power?      [1996]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 15

We know that  

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 16

If fV and fR are the focal lengths of a convex lensfor violet and red light respectively and FV and FR are the focal lengths of concave lens for violetand red light respectively, then we have [1996]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 16

According to Cauchy relation

Hence, red light having maximum wavelength
has maximum focal length.

∴ fv < fr and also Fv > Fr as focal length is
negative for a concave lens.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 17

Light travels through a glass plate of thickness t and refractive index μ. If c is the speed of light in vacuum, the time taken by light to travel this thickness of glass is

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 17

Total thickness = t; Refrative index = μ

Speed of light in Glass plate = c/μ

[where, t = thickness of glass plate]

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 18

One face of a rectangular glass plate 6 cm thick issilvered. An object held 8 cm in front of the firstface forms an image 12 cm behind the silveredface. The refractive index of the glass is [1996]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 18

Thickness of glass plate (t) = 6 cm;
Distance of the object (u) = 8 cm.
And distance of the image (v) = 12 cm.
Let x = Apparent position of the silvered
surface in cm.
Since the image is formed due to relfection at
the silvered face and by the property of mirror
image
Distance of object from the mirror = Distance
of image from the mirror
or, x + 8 = 12 + 6 – x ⇒ x = 5 cm.
Therefore, refractive index of glass

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 19

The focal length of converging lens is measuredfor violet, green and red colours. It is respectively fv, fg, fr. We will get [1997]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 19

According to Cauchy relation

∴ Red light has wavelength greater than
violet light. Therefore focal length of lens
for red is greater than for violet. (fr > fv)

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 20

An astronomical telescope has a length of 44 cmand tenfold magnification. The focal length ofthe objective lens is [1997]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 20

Given : Length of astronomical telescope
(f0 + fe) = 44 cm and magnification

From the given magnification, we find that f0
= 10fe. Therefore, 10fe + fe = 44 or 11fe = 44 or
fe = 4. And focal length of the objective
(f0) = 44 – fe = 44 – 4 = 40 cm.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 21

An electromagnetic radiation of frequency n, wavelength λ, travelling with velocity v in air enters in a glass slab of refractive index (ν). The frequency, wavelength and velocity of light in the glass slab will be respectively [1997]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 21

When electromagnetic wave enters in other
medium, frequency reamains unchanged
while wavelength and velocity become 1/μ times.

So, For e.m. wave entering from air to glass
slab (μ), frequency remains n,

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 22

A luminous object is placed at a distance of 30 cm from the convex lens of focal length 20 cm. On theother side of the lens, at what distance from thelens a convex mirror of radius of curvature 10 cmbe placed in order to have an upright image of theobject coincident with it? [1998]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 22

For the lens,

Coincidence is possible when the image is
formed at the centre of curvature of the
mirror. Only then the rays refracting through
the lens will fall normally on the convex mirror
and retrace their path to form the image at O.
So, the distance between lens and mirror
= 60 – 10 = 50 cm.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 23

Light enters at an angle of incidence in atransparent rod of refractive index n. For whatvalue of the refractive index of the material ofthe rod the light once entered into it will notleave it through its lateral face whatsoever bethe value of angle of incidence? [1998]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 23

Let a ray of light enter at A and the refracted
beam is AB. This is incident at an angle θ.
For no refraction at the lateral face, θ > C
or, sin θ > sin C But θ+ r =90°⇒θ= (90° – r)

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 24

A plano-convex lens is made of material ofrefractive index 1.6. The radius of curvature ofthe curved surface is 60 cm. The focal length ofthe lens is [1999]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 24

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 25

Wavelength of light of frequency 100 Hz [1999]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 25

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 26

The refractive index of the material of the prismis √3 ; then the angle of minimum deviation ofthe prism is [1999]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 26

Angle of minimum deviation

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 27

The radius of curvature of a thin plano-convexlens is 10 cm (of curved surface) and the refractiveindex is 1.5. If the plane surface is silvered, thenit behaves like a concave mirror of focal length   [2000]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 27

The silvered plano convex lens behaves as a
concave mirror; whose focal length is given by

If plane surface is silvered

 

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 28

A person is six feet tall. How tall must a verticalmirror be if he is able to see his entire length?

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 28

To see his full image in a plane mirror a person
requires a mirror of at least half of his height.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 29

Rainbow is formed due to a combination of   [2000]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 29

Rainbow is formed due to combination of
total internal reflection and dispersion.

31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 30

An air bubble in a glass slab (μ = 1.5) is 5 cmdeep when viewed from one face and 2 cm deepwhen viewed from the opposite face. Thethickness of the slab is [2000]

Detailed Solution for 31 Year NEET Previous Year Questions: Ray Optics & Optical Instruments - 2 - Question 30

∴ Thickness of the slab = R1 + R2
= 7.5 + 3 = 10.5 cm

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