Chapter– 10 Optical Instruments

TOPIC WISE MULTIPLE CHOICE QUESTIONS

10.1 LEAST DISTANCE OF DISTINCT VISION

(1) The minimum distance from the eye at which an object appears to be distinct is
called
(a) infinite point (b) least distance of fuzzy vision
(c) least distance of distinct vision (d) none of these
(2) The least distance of distinct vision for the normal eye is LHR-2016 (G-II)
(a) 25cm (b) 2.5cm
(c) 15cm (d) 20cm
(3) The least distance of distinct vision
(a) decreases with age (b) increases with age
(c) no change (d) none of these
(4) A human eye acts like
(a) mirror (b) lens
(c) laser (d) all of these
(5) Far point for the human eye is
(a) 10cm (b) 25cm
(c) 20cm (d) infinity
10.2 MAGNIFYING POWER AND RESOLVING POWER OF OPTICAL
INSTRUMENTS
(6) Product of number of rulings “N” and the order of diffraction “m” is equal to:
LHR-2019 (G-II)
(a) Resolving power (b) Magnification
(c) Near point (d) Magnifying power
(7) Rayleigh formula for resolving power SGD-2016 (G-I)

(a) R 1.22 D (b) R 1.22D

(c) R  D1.22 (d) R 1.22D

(8) The ratio of the angles subtended by the image as seen through the optical device to
that subtended by the object at the unaided eye is called
(a) linear magnification (b) least distance of distinct vision
(c) angular magnification (d) near point
(9) The power of lens is measured in
(a) joule (b) diopter
(c) watt (d) meters
(10) Unit of magnification
(a) meter (b) diopter

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(c) cm 10 (d) no unit Instruments

(11) To increase the resolving power of lens

(a) increase λ and D (b) increase λ and decrease D
(c) decrease λ and increase D (d) decrease λ and D
(12) The resolving power of diffraction grating is defined as
 
(a) (b)
 
(c)  1  2 (d)   2 1

 
(13) The ratio of the size of the image to the size of object is called
(a) magnification (b) angular magnification
(c) classification (d) linear classification
(14) When an object is viewed at a shorter distance, the image on the retina of the eye is
(a) smaller (b) greater
(c) unchanged (d) remain same
(15) The resolving power of an optical instrument can be expressed
1
(a) R = (b) R = αmax
α
min

(c) R = αres (d) R = α

(16) Magnification of a lens is negative when the image is
(a) real and inverted (b) real and erected
(c) virtual and inverted (d) virtual and erect
(17) Wavelength of light used in an optical instrument are λ1= 4000 Å and λ2 = 5000 Å,
then ratio of their respective resolving powers (corresponding to λ1 and λ2 ) is
(a) 16 : 25 (b) 9 : 1
(c) 4 : 5 (d) 5 : 4
(18) When the image is real and inverted the magnification of the lens is
(a) positive (b) neutral
(c) negative (d) virtual
(19) The smaller value of αmin ___________ is the resolving power.
(a) smaller (b) greater
(c) zero (d) none of these
(20) A magnifying glass has a focal length of 15 cm. If the near point of the eye is 25 cm
from the eye the angular magnification of the glass is about:
(a) 0.067 (b) 0.33
(c) 2.7 (d) 1.7
(21) A good optical device should have
(a) high magnification power and high resolving power

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(b) Low magnification power and high resolving power

(c) Low magnification power and Low resolving power
(d) high magnifications power and low resolving power
10.3 SIMPLE MICROSCOPE
(22) The magnifying power of convex lens of focal length 10cm is: GRW-2019 (G-I)
(a) 7 (b) 9.6
(c) 3.5 (d) 11
(23) The magnifying power of a magnifying glass is: BWP-2019 (G-I) d f
(a) 1 (b) 1 f d
f d (c) (d) 1 d f
(24) The magnification of a convex lens of focal length 5cm is equal toMTN-2018 (G-I)

(a) (b) 5
(c) 6 (d) 25
(25) The magnifying power of a simple microscope is BWP-2016 (G-I) f
d (a) M  1 (b) M  1 d f
1
(c) M  1 (d) M  1 df
f
(26) If a convex lens is used as a magnifying glass, which lens will give higher
magnification that has DGK-2016 (G-I)
(a) short size (b) long focal length
(c) large size (d) short focal length
(27) Watch makers uses
(a) convex lens (b) concave lens
(c) plano-concave lens (d) mirror
(28) Focal length of convex lens will be maximum for
(a) blue light (b) red light
(c) green light (d) yellow light
(29) If the image is at the least distance of the distinct vision then
(a) q = d (b) q= 1/d
(c) 1/q = d (d) q – d = 1
(30) In a simple microscope, if final image is located at infinity then its magnifying power
is
25 25 f 25 (a) (b) (c) (d) 1 f D 25 f
(31) If the object is 5mm high and image is 2cm high then the magnification is
(a) 4 (b) 1
(c) 2 (d) 10
(32) For a lens of high magnification the focal length should be
(a) large (b) small
(c) of any size (d) none of these
(33) If f = 5cm then the magnification of the simple microscope will be

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 (a) M = 4 (b) M = 6
(c) M = 5 (d) M = 2
(34) In magnifying glass, the object is placed at
(a) Focus (b) Between f and 2f
(c) Beyond 2f (d) Between lens and f
(35) The magnifying power of a magnifying glass of focal length of 25cm will be
(a) 5 (b) 2 (c) 6 (d) 0

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Chapter–
(36) When beam of white light falls perpendicularly on a plane of glass then the angle of
refraction will be
(a) 90o (b) 60o
(c) 0° (d) 180o
(37) The image formed by the simple microscope is
(a) inverted and real (b) erect and virtual
(c) real and erect (d) inverted and magnified
(38) If f = 50cm and the final image is formed at d = 25 cm, the magnifying power of
simple microscope:
(a) 5 (b) 3/2
(c) 0 (d) 1
10.4 COMPOUND MICROSCOPE
(39) The focal length of the objective used in compound microscope
(a) large (b) small
(c) same as eyepiece (d) none of these
(40) The magnifying power of compound microscope
q q  d  (a) M  1df 
e (b) M  1  p
p  fe 

(c) M  qp 1 dfe  (d) M  qp 1 dfe 


(41) The image formed by the eyepiece of compound microscope is
(a) real and inverted (b) real and erect
(c) virtual and erect (d) virtual and inverted
(42) The resolving power of a compound microscope depends upon
(a) the refractive index of the medium in which object is placed
(b) diameter of objective
(c) width of objective lens
(d) nature of lens
(43) The angular magnification of the compound microscope is defined by

(a) tano (b) tane tane tano

1
(c) tan e tan o (d)
tan e tan o
(44) For higher magnification which of the following instrument is used
(a) optical fiber (b) compound microscope
(c) collimator (d) LED
(45) The diverging lens of compound microscope is
(a) eyepiece (b) objective
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(c) eye (d) none of these

(46) The magnifying power of compound microscope is given by the relation
(a) Mo -Me (b)Mo Me
(c) Mo + Me (d) Mo/Me
(47) The magnification of two lenses of compound microscope are 2 and 5 then
magnifying power of microscope is
(a) 7 (b) 3
(c) 10 (d) 20
(48) The compound microscope is based on the principle of
(a) reflection (b) refraction
(c) both a & b (d) none of these
(49) In a compound microscope magnification produced by objective is 5 and that
produced by eye piece is 50, the total magnification produced by the microscope is
(a) 250 times (b) 10 times
(c) 25 times (d) 100 times
10.5 ASTRONOMICAL TELESCOPE
(50) If f =100cm;f =5cmo e length and magnifying power of an astronomical
telescope
is:
LHR-2019 (G-I)
(a) 0.05cm ; 20 (b) 95 cm ; 20
(c) 20cm ; 500 (d) 105 cm ; 20
(51) Magnifying power of telescope is: LHR 2015(G-II) fe
fo
(a) (b) fo fe
1
(c) f fe o (d)
f fe o
(52) For formal adjustment what is the length of astronomical telescope of focal lengths
of objective and eye-piece are 100 and 20 cm respectively. DGK-2018 (G-I)
(a) 100 cm (b) 20 cm
(c) 5 cm (d) 120 cm
(53) If focal length of objective and eye piece is 0.5 m and 10 cm respectively then
magnifying power of telescope will be SWL-2017
(a) 5 (b) 0.5
(c) 10 (d) 20
(54) The final image seen from the astronomical telescope
(a) real, erect and enlarged (b) real, inverted and enlarged
(c) virtual, inverted and enlarged (d) virtual, erect and enlarged
(55) In astronomical telescope the image formed by eyepiece is
(a) real (b) virtual
(d)

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(c) neither real nor virtual (d) none of these
(56) A simple astronomical telescope consists of
(a) two concave lenses (b) two convex lenses
(c) one concave and one convex lens (d) two plano-concave lens
(57) The rays after refraction through the eye piece will become parallel and the final
image appears to be formed at
(a) f (b) 2f
(c) between f and 2f (d) infinity
(58) The resolving power of an astronomical telescope depends on
(a) the focal length of the objective lens
(b) the least distance of distinct vision of the observer
(c) the focal length of the eyepiece
(d) the diameter of the objective lens

Chapter–
(59) For normal adjustment the distance between the objective and eye-piece of a
telescope is
(a) fo + fe (b) fo – fe
(c) fe – fo (d) none of these
(60) In simple astronomical telescope the focal length of objective is
(a) less than eyepiece (b) greater than eye piece
(c) equal to eyepiece (d) none of these
(61) In astronomical telescope, if the focal lengths of objective and eye piece is 35 cm and
5cm respectively, then its length for normal adjustment is
(a) 40cm (b) 35cm
(c) 4.5cm (d) 3.5cm
(62) A good telescope used by astronomers has an objective of
(a) long focal length and small aperture (b) small focal length and large aperture
(c) long focal length and of large aperture (d) small focal length and small aperture
(63) The focal length of the objective of telescope (fo) can be expressed as
M fe
(a) (b) fe M
1
(c) M  fe (d)
Mfe 10.6
SPECTROMETER
(64) Which is not the essential component of a spectrometer? (FSD 2015)
(a) collimator (b) telescope
(c) turntable (d) microscope
(65) An optical device used to study spectra from different sources of light is called
(a) micrometer (b) spectrometer
(c) collimator (d) telescope
(66) Spectrometer consists of
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(a) four parts (b) three parts (c) five parts (d) two parts
(67) In spectrometer the function of collimator is to produce
(a) parallel beam of light (b) converging beam of light
(c) diverging beam of light (d) all of these
(68) A fixed metallic tube with a convex lens at one end of the spectrometer is called
(a) telescope (b) microscope
(c) collimator (d) periscope
(69) The grating placed on the turn table which is capable of rotating about
(a) horizontal axis (b) vertical axis
(c) both a & b (d) in all direction
(70) A circular scale of the spectrometer, graduated in
(a) 180° (b) 90°
(c) half degree (d) 360°
(71) The resolving power of spectrometer of “N” number of rulings is expressed as
m
(a) R = N + m (b) R =
N
(c)R  N m none of these

(d)

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Chapter–
10.7 SPEED OF LIGHT
(72) In Michelson’s experiment, the angle subtended by a side of the eight sided mirror
is: FSD-2017

 
(a) rad (b) rad
8 4


(c) rad (d)
2
(73) Who was the first person to make attempt to measure the speed of light
(a) Michelson (b) Galileo
(c) Einstein (d) Newton
(74) The speed of light in materials other than vacuum is always
(a) greater than c (b) less than c
(c) equal to c (d) none of these
(75) Michelson’s formula for the speed of light is
16 f 16d (a) c  (b) c  d f
fd
(c) c 16fd (d) c 
16
(76) The speed of light in the medium of refractive index of 1.5 is
(a) 2 x 108ms-1 (b) 3 x 108ms-1
(c) 0.5 x 108ms-1 (d) 1.5 x 108ms-1
(77) The speed of light in vacuum is
(a) 3 × 105kms–1 (b) 3 × 10–8ms–1
(c) 3 × 108kms–1 (d) 3 × 106ms–1
(78) The speed of light in air
(a) very less than in vacuum (b) very greater than in vacuum
(c) nearly equal to in vacuum (d) zero
(79) The speed of light in diamond is 1.5 x 108ms-1 its refractive index w.r.t to air is
(a) 1 (b) 3
(c) 1.5 (d) 2
10.8 INTRODUCTION OF FIBRE OPTICS
(80) Information carrying capacity of fibre optics is known as
LHR-2016 (G-I), LHR-2018 (G-II)
(a) semiconductor (b) band length
(c) bandwidth (d) laser
(81) Photo phone was invented by

(d)

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(a) Graham Bell (b) Alexander Fleming
(c) Galileo (d) Abu Ali Sena
(82) The practical use of services of optical fibre is
(a) telecommunication
(b) word processing
(c) image transmission and receiving equipment (d) all of these
(83) Which light can travel faster through the optical fibre
(a) infra red (b) ultraviolet
(c) visible none of these

(84) Characteristic of optical fibre is

(a) much thinner (b) light weight
(c) extremely wide bandwidth (d) all of these
(85) Graham Bell was able to transmit a voice message via
(a) microscope (b) periscope
(c) beam of light (d) telescope
(86) The detector used in photo phone is made of
(a) selenium (b) copper
(c) curie (d) aluminum
(87) With respect to efficiency an optical fibre of diameter 6mm, can replace the bundle
of
(a) copper of 7.62cm (b) aluminum wire of 7.62cm
(c) copper of 6.72cm (d) aluminum wire of 6.34cm
10.9 FIBRE OPTIC PRINCIPLES
(88) If the speed of light in vacuum is c, then its velocity in a medium of refractive index
1.3 is: LHR-2017 (G-II)
1.3
(a) 1.3c (b)
c
c
(c) (d) c
1.3
(89) Critical angle is that incident angle in denser medium for which angle of refraction
is (GRW 2014)
(a) 0 (b) 45
(c) 180 (d) 90
c
(90) The ratio is equal to: MTN-2019 (G-II)
v
(a) Critical angle (b) Total reflection
(c) Refractive index (d) Angle of refraction

(d)

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(91) For glass air boundary, the value of critical angle is: SWL-2016 (G-I)
(a)41.4o (b)41.6o
(c)41.8o (d)42.2o

(92) Snell’s law is expressed as

1
(a) sinc  (b) n1 sin1  n2 sin2
n n2 1

(c) n1 sin1  0 (d) n2 sin2  0 n2 sin2 n1 sin1

(93) Cladding is the layer of lower refractive index over central core of
(a) small refractive index (b) high refractive index
(c) zero refractive index (d) none of these
(94) When the light enters in the glass, there is no change in its
(a) velocity (b) wavelength
(c) frequency (d) direction
(95) The main drawback of multimode step index fibre is
(a) quality of fibre (b) size of cable
(c) dispersion of signal amount of data

Chapter–
(96) For the protection, the optical fibre is covered with
(a) glass jacket (b) copper jacket
(c) plastic jacket (d) rubber jacket
(97) When a ray passes through the denser medium to the rarer medium the refracting
ray
(a) bends towards the normal (b) bends away from the normal
(c) moves along to the normal (d) none of these
(98) Now a days, a new type of optical fibre is used in which the central core has
(a) high density (b) low density
(c) low refractive index (d) zero refractive index
(99) To obey the phenomenon of total internal reflection, the angle of incidence of ray
(a) should be greater than critical angle (b) should be less than critical angle
(c)should be equal to critical angle (d) should be zero
(100) A ray which passes through the rigid rod (glass rod) and parallel to the axis of rigid
rod is called
(a) reflected ray (b) axial ray
(c) no-axial ray (d) X-rays
(101) The optical fibre whose density gradually decreases towards its periphery is called
(a) single mode step index fibre (b) multimode graded index fibre
(c) multimode step index fibre (d) single graded step index fibre
(102) Snell’s law helps to find
(a) frequency of light (b) wavelength of light

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(c) refractive index of any material (d) none of these
(103) When θ2 = 90° and θ1 = θC then Snell’s law becomes n1
(a) sin c n n1 2 (b) sin c
n2

n2 (d) sin c 1
(c) sin c
n1 n n12

(d)

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