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CHAPTER 10:Optical Instruments

(1)               A lens which converges a beam of parallel rays to a point is called
(a)    Diverging (or concave) lens
(b)   Converging (or convex) lens
(c)    Plano concave lens
(d)   Plano convex lens

(2)               A point where the incident parallel rays of light converge or appear to diverge after passing through a lens is called
(a)    Center of curvature
(b)   Focus
(c)    Optical centre
(d)   Aperture

(3)               The diameter of a lens is called
(a)    Focal length
(b)   Principal axis
(c)    Aperture
(d)   Radius of curvature

(4)               In going form a denser to rarer medium a array of light is
(a)    undeviated
(b)   bent away form the normal
(c)    bent towards the normal
(d)   polarized

(5)               Unit of power of a lens is
(a)  Meter
(b)  watt
(c)  dioptre
(d)  horsepower

     (6)         Dioptre power of an concave lens of 10 cm focal length is
(a)    10 dioptre
(b)   -10 dioptre
(c)    1/10 dioptre
(d)   -1/10 dioptre

    (7)         The power of a concave lens is
(a)    real
(b)    virtual
(c)    positive
(d)    negative

(8)               The minimum distance between an object and its real image in a convex lens is
a.       2 f
b.      2.5 f
c.       3 f
d.      4f

(9)               If an object is placed away form ‘2f’ of a converging lens, then the image will be
a.       Real and erect
b.      Virtual and erect
c.       Real and inverted
d.      Virtual
(10)           A convex lens gives a virtual image only when the objects leis
a.       Between principal focus and center of curvature
b.      Beyond 2 f
c.       At the principal focus
d.      Between principal focus and optical center

(11)           Magnifying power of simple microscope
a.       Increase with increase in focal length
b.      Increase with decrease in focal length
c.       No effect with decrease or increase with focal length
d.      List distance of distinct vision

(12)           Image of an object 5 mm high is only 1 cm high. Magnification produced by lens is
a.       0.5
b.      0.2
c.       1
d.      2

(13)           The least distance of distinct vision for a normal eye is
a.       15cm
b.      25cm
c.       30cm
d.      40cm

(14)           least distance of distinct vision
a.       increases with increase in age
b.      decrease with increaser in age
c.       neither increases nor decreases
d.      becomes infinite after 60 years

(15)           If a convex lens of large aperture fails to converge the light rays incident on it to a single point, it is said to suffer form
a.       Chromatic aberration
b.      Spherical aberration
c.       Both spherical and chromatic
d.      Distortion

(16)           Two convex lenses of equal focal length ‘f’  are placed in contact, the resultant focal length of the combination is
a.       Zero
b.      f
c.       2f
d.      f/2

(17)           A convex lens of focal length ‘f1’and a concave lens of focal length ‘f2’ are placed in contact. The focal length of the combination is
a.       f2 + f1
b.      f2 – f1
c.       f1f2/f2+f1
d.      f1f2/f1-f2

(18)           Final image produced by a compound microscope  is
a.       Real and inverted
b.      Real and erect
c.       Virtual and erect
d.      Virtual and inverted.

(19)           for normal adjustment, length of astronomical telescope is
a.       fo + fe
b.      fo – fe
c.       fo/fe
d.      fe/fo

(20)           In multimode step index fibre the refractive index of core and cladding is
a.       Same
b.      Different
c.       Zero
d.      Different with refractive index of core higher than cladding

(21)           Dispersional effect may produced error in light signals. This type of error is minimum in.
a.       Single mode step index fibre
b.      Multimode step index fibre
c.       Multimode graded index fibre
d.      Monomode step index fibre

(22)           Light signals passes through multimode graded fibre due to .
a.       Continuous refraction
b.      Total internal reflection
c.       Both continuous refraction and total internal reflection 
d.      Diffraction

(23)           Which one type of fibre is more suitable for transmission of signals in which white light is used?
a.       Mono mode step index fibre
b.      Multi mode step index fibre
c.       Multi mode graded index fibre
d.      Single mode step index fibre

(24)           Critical angle is that incident angle in denser medium for which angle of refraction is.
a.       0o
b.      45 o
c.       90 o
d.      180 o

(25)           There is no noticeable boundary between core and cladding.
a.       Multi mode step index fibre
b.      Multi mode graded index fibre
c.       Single mode step index fibre
d.      All types of fibre

(26)           The electrical signals change into light signals for transmission through optical fibre. A light pulse represent.
a.       Zero (0)
b.      One (1)
c.       Both zero (0) and one (1)
d.      Neither zero (0) nor one (1)

(27)           A lens, which is thicker at the center and thicker at the edges, is called.
a.       Concave lens
b.      Convex lens
c.       Plano convex lens
d.      Plano concave lens

(28)           A spectrometer is used to find.
a.       Wave length of light
b.      Refractive index of the prism
c.       Wavelength of different colours
d.      None
(29)           If a convex lens of focal length ‘f’ is cut into two identical halves along the lens diameter, the focal length of each half is.
a.       f
b.      f/2
c.       2f
d.      3f/2

(30)           A convex and concave lens of focal length ‘f’ are in contact, the focal length of the combination will be.
a.       Zero
b.      f/2
c.       2f
d.      Infinite

(31)      A double convex lens acts as a diverging lens when the object is placed
                  (a) at the focus                   (b)  at 2f         
                  (c) between f and 2f                      (d)  within the focal length

(32)      The least distance of distinct vision for normal eye is approximately
            (a)  10 cm                          (b) 15 cm        
            (c)  20 cm                          (d)  25 cm

(33)      White light does not focus to a single point after passing through a convex lens due to
(a)    chromatic aberration               
                  (b) spherical aberration   
                  (c) distortion                                   
                  (d) spherical and chromatic aberrations

(34)      Chromatic aberration can be removed by using
(a)    concave lens               
(b) combination of concave and convex lenses
            (c) two convex lenses       
            (d) two concave lenses

(35)      Spherical aberration can be reduced by using
(a)    double convex lens                 
(b) central portion of the lens       
            (c) edge portion of the lens           
            (d)  parallel rays

(36)      If placed in contact, the focal length of the combination of two convex lenses of equal focal lengths f, will be
            (a) zero                 (b)  f/2            
            (c)  f                      (d)  2f

(37)      If a single convex lens is placed close to the eye, it can be used as a
(a)    telescope         
(b) simple microscope   
(c) compound microscope            
                  (d) refracting telescope

(38)      If d is the distance of distinct vision, the magnifying power of a magnifying glass of focal length f is
(a) d/f                   (b)  f/d            
(c) 1 + d/f              (d) 1 + f/d
(39)            The objective of a microscope is a lens of
                  (a) large focal length and converging properties
                  (b) moderate focal length and diverging properties
                  (c) very short focal length and converging properties
                  (d) moderate focal length and converging properties
(40)      The magnifying power of a compound microscope in terms of the magnification of the objective and magnifying power of the eyepiece is given by
(a) M =         (b)  
(c)               (d)  


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