
question_answer1) If luminous efficiency of a lamp is 2 lumen/watt and its luminous intensity is 42 candela, then power of the lamp is [AFMC 1998]
A) 62 W done
clear
B) 76 W done
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C) 138 W done
clear
D) 264 W done
clear
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question_answer2) An electric bulb illuminates a plane surface. The intensity of illumination on the surface at a point 2m away from the bulb is \[5\times {{10}^{4}}\] phot (lumen/cm2). The line joining the bulb to the point makes an angle of 60o with the normal to the surface. The intensity of the bulb in candela is [IITJEE 1980; CPMT 1991]
A) \[40\sqrt{3}\] done
clear
B) 40 done
clear
C) 20 done
clear
D) \[40\times {{10}^{4}}\] done
clear
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question_answer3) In a movie hall, the distance between the projector and the screen is increased by 1% illumination on the screen is [CPMT 1990]
A) Increased by 1% done
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B) Decreased by 1% done
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C) Increased by 2% done
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D) Decreased by 2% done
clear
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question_answer4) Correct exposure for a photographic print is 10 seconds at a distance of one metre from a point source of 20 candela. For an equal fogging of the print placed at a distance of 2 m from a 16 candela source, the necessary time for exposure is
A) 100 sec done
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B) 25 sec done
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C) 50 sec done
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D) 75 sec done
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question_answer5) A bulb of 100 watt is hanging at a height of one meter above the centre of a circular table of diameter 4 m. If the intensity at a point on its rim is \[{{I}_{0}}\], then the intensity at the centre of the table will be [CPMT 1996]
A) \[{{I}_{0}}\] done
clear
B) \[2\sqrt{5}{{I}_{0}}\] done
clear
C) \[2{{I}_{0}}\] done
clear
D) \[5\sqrt{5}{{I}_{0}}\] done
clear
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question_answer6) A movie projector forms an image 3.5m long of an object 35 mm. Supposing there is negligible absorption of light by aperture then illuminance on slide and screen will be in the ratio of [CPMT 1982]
A) 100 : 1 done
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B) 104 : 1 done
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C) 1 : 100 done
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D) 1 : 104 done
clear
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question_answer7) A 60 watt bulb is hung over the center of a table 4 m ? 4 m at a height of 3 m. The ratio of the intensities of illumination at a point on the centre of the edge and on the corner of the table is [CPMT 1976, 84]
A) \[{{(17/13)}^{3/2}}\] done
clear
B) 2 / 1 done
clear
C) 17 / 13 done
clear
D) 5 / 4 done
clear
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question_answer8) "Lux" is a unit of [Kerala PMT 2001]
A) Luminous intensity of a source done
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B) Illuminance on a surface done
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C) Transmission coefficient of a surface done
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D) Luminous efficiency of source of light done
clear
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question_answer9) Total flux produced by a source of 1 cd is [CPMT 2001]
A) \[\frac{1}{4\pi }\] done
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B) \[8\pi \] done
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C) \[4\pi \] done
clear
D) \[\frac{1}{8\pi }\] done
clear
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question_answer10) If the luminous intensity of a 100 W unidirectional bulb is 100 candela, then total luminous flux emitted from the bulb is [AIIMS 1998]
A) 861 lumen done
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B) 986 lumen done
clear
C) 1256 lumen done
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D) 1561 lumen done
clear
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question_answer11) The maximum illumination on a screen at a distance of 2 m from a lamp is 25 lux. The value of total luminous flux emitted by the lamp is [JIMPER 1997]
A) 1256 lumen done
clear
B) 1600 lumen done
clear
C) 100 candela done
clear
D) 400 lumen done
clear
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question_answer12) A small lamp is hung at a height of 8 feet above the centre of a round table of diameter 16 feet. The ratio of intensities of illumination at the centre and at points on the circumference of the table will be [CPMT 1984, 1996]
A) 1 : 1 done
clear
B) 2 : 1 done
clear
C) \[2\sqrt{2}:1\] done
clear
D) 3 : 2 done
clear
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question_answer13) Lux is equal to [CPMT 1993]
A) 1 lumen/m2 done
clear
B) 1 lumen/cm2 done
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C) 1 candela/m2 done
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D) 1 candela/cm2 done
clear
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question_answer14) Five lumen/watt is the luminous efficiency of a lamp and its luminous intensity is 35 candela. The power of the lamp is [CPMT 1992]
A) 80 W done
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B) 176 W done
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C) 88 W done
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D) 36 W done
clear
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question_answer15) A lamp rated at 100 cd hangs over the middle of a round table with diameter 3 m at a height of 2 m. It is replaced by a lamp of 25 cd and the distance to the table is changed so that the illumination at the centre of the table remains as before. The illumination at edge of the table becomes X times the original. Then X is [CPMT 1989]
A) \[\frac{1}{3}\] done
clear
B) \[\frac{16}{27}\] done
clear
C) \[\frac{1}{4}\] done
clear
D) \[\frac{1}{9}\] done
clear
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question_answer16) The distance between a point source of light and a screen which is 60 cm is increased to 180 cm. The intensity on the screen as compared with the original intensity will be [CPMT 1888]
A) (1 / 9) times done
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B) (1 / 3) times done
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C) 3 times done
clear
D) 9 times done
clear
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question_answer17) A source of light emits a continuous stream of light energy which falls on a given area. Luminous intensity is defined as [CPMT 1986]
A) Luminous energy emitted by the source per second done
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B) Luminous flux emitted by source per unit solid angle done
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C) Luminous flux falling per unit area of a given surface done
clear
D) Luminous flux coming per unit area of an illuminated surface done
clear
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question_answer18) Venus looks brighter than other stars because [MNR 1985]
A) It has higher density than other stars done
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B) It is closer to the earth than other stars done
clear
C) It has no atmosphere done
clear
D) Atomic fission takes place on its surface done
clear
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question_answer19) To prepare a print the time taken is 5 sec due to lamp of 60 watt at 0.25 m distance. If the distance is increased to 40 cm then what is the time taken to prepare the similar print [CPMT 1982]
A) 3.1 sec done
clear
B) 1 sec done
clear
C) 12.8 sec done
clear
D) 16 sec done
clear
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question_answer20) A lamp is hanging 1 m above the centre of a circular table of diameter 1m. The ratio of illuminaces at the centre and the edge is [NCERT 1982]
A) \[\frac{1}{2}\] done
clear
B) \[{{\left( \frac{5}{4} \right)}^{\frac{3}{2}}}\] done
clear
C) \[\frac{4}{3}\] done
clear
D) \[\frac{4}{5}\] done
clear
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question_answer21) Two stars situated at distances of 1 and 10 light years respectively from the earth appear to possess the same brightness. The ratio of their real brightness is [NCERT 1981]
A) 1 : 10 done
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B) 10 : 1 done
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C) 1 : 100 done
clear
D) 100 : 1 done
clear
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question_answer22) The intensity of direct sunlight on a surface normal to the rays is \[{{I}_{0}}\]. What is the intensity of direct sunlight on a surface, whose normal makes an angle of 60o with the rays of the sun [CPMT 1981]
A) \[{{I}_{0}}\] done
clear
B) \[{{I}_{0}}\left( \frac{\sqrt{3}}{2} \right)\] done
clear
C) \[\frac{{{I}_{0}}}{2}\] done
clear
D) \[2{{I}_{0}}\] done
clear
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question_answer23) Inverse square law for illuminance is valid for [CPMT 1978]
A) Isotropic point source done
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B) Cylindrical source done
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C) Search light done
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D) All types of sources done
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question_answer24) 1% of light of a source with luminous intensity 50 candela is incident on a circular surface of radius 10 cm. The average illuminance of surface is
A) 100 lux done
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B) 200 lux done
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C) 300 lux done
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D) 400 lux done
clear
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question_answer25) Two light sources with equal luminous intensity are lying at a distance of 1.2 m from each other. Where should a screen be placed between them such that illuminance on one of its faces is four times that on another face
A) 0.2 m done
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B) 0.4 m done
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C) 0.8 m done
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D) 1.6 m done
clear
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question_answer26) Two lamps of luminous intensity of 8 Cd and 32 Cd respectively are lying at a distance of 1.2 m from each other. Where should a screen be placed between two lamps such that its two faces are equally illuminated due to two sources
A) 10 cm from 8 Cd lamp done
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B) 10 cm from 32Cd lamp done
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C) 40 cm from 8 Cd lamp done
clear
D) 40 cm from 32 Cd lamp done
clear
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question_answer27) A lamp is hanging along the axis of a circular table of radius r. At what height should the lamp be placed above the table, so that the illuminance at the edge of the table is \[\frac{1}{8}\] of that at its center [MP PET 2005]
A) \[\frac{r}{2}\] done
clear
B) \[\frac{r}{\sqrt{2}}\] done
clear
C) \[\frac{r}{3}\] done
clear
D) \[\frac{r}{\sqrt{3}}\] done
clear
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question_answer28) A point source of 100 candela is held 5m above a sheet of blotting paper which reflects 75% of light incident upon it. The illuminance of blotting paper is
A) 4 phot done
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B) 4 lux done
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C) 3 phot done
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D) 3 lux done
clear
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question_answer29) A lamp is hanging at a height 40 cm from the centre of a table. If its height is increased by 10 cm the illuminance on the table will decrease by
A) 10 % done
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B) 20% done
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C) 27% done
clear
D) 36% done
clear
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question_answer30) Which has more luminous efficiency
A) A 40 W bulb done
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B) A 40 W fluorescent tube done
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C) Both have same done
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D) Cannot say done
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question_answer31) An electric lamp is fixed at the ceiling of a circular tunnel as shown is figure. What is the ratio the intensities of light at base A and a point B on the wall
A) 1 : 2 done
clear
B) \[2:\sqrt{3}\] done
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C) \[\sqrt{3}:1\] done
clear
D) \[1:\sqrt{2}\] done
clear
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question_answer32) When sunlight falls normally on earth, a luminous flux of \[1.57\times {{10}^{5}}\ lumen/{{m}^{2}}\] is produced on earth. The distance of earth from sun is \[1.5\times {{10}^{8}}Km\]. The luminous intensity of sun in candela will be
A) \[3.53\times {{10}^{27}}\] done
clear
B) \[3.53\times {{10}^{25}}\] done
clear
C) \[3.53\times {{10}^{29}}\] done
clear
D) \[3.53\times {{10}^{21}}\] done
clear
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question_answer33) In the above problem, the luminous flux emitted by sun will be
A) \[4.43\times {{10}^{25}}\ lm\] done
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B) \[4.43\times {{10}^{26}}\ lm\] done
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C) \[4.43\times {{10}^{27}}\ lm\] done
clear
D) \[4.43\times {{10}^{28}}\ lm\] done
clear
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question_answer34) A screen receives 3 watt of radiant flux of wavelength 6000 A. One lumen is equivalent to \[1.5\times {{10}^{3}}watt\] of monochromatic light of wavelength 5550 A. If relative luminosity for 6000 A is 0.685 while that for 5550 A is 1.00, then the luminous flux of the source is
A) \[4\times {{10}^{3}}lm\] done
clear
B) \[3\times {{10}^{3}}lm\] done
clear
C) \[2\times {{10}^{3}}lm\] done
clear
D) \[1.37\times {{10}^{3}}lm\] done
clear
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question_answer35) A point source of 3000 lumen is located at the centre of a cube of side length 2m. The flux through one side is
A) 500 lumen done
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B) 600 lumen done
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C) 750 lumen done
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D) 1500 lumen done
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question_answer36) Light from a point source falls on a small area placed perpendicular to the incident light. If the area is rotated about the incident light by an angle of 60o, by what fraction will the illuminance change
A) It will be doubled done
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B) It will be halved done
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C) It will not change done
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D) It will become onefourth done
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question_answer37) A point source of light moves in a straight line parallel to a plane table. Consider a small portion of the table directly below the line of movement of the source. The illuminance at this portion varies with its distance r from the source as
A) \[E\propto \frac{1}{r}\] done
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B) \[E\propto \frac{1}{{{r}^{2}}}\] done
clear
C) \[E\propto \frac{1}{{{r}^{3}}}\] done
clear
D) \[E\propto \frac{1}{{{r}^{4}}}\] done
clear
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question_answer38) Figure shows a glowing mercury tube. The illuminances at point A, B and C are related as
A) B > C > A done
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B) A > C > B done
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C) B = C > A done
clear
D) B = C < A done
clear
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question_answer39) The relative luminosity of wavelength 600 nm is 0.6. Find the radiant flux of 600 nm needed to produce the same brightness sensation as produced by 120 W of radiant flux at 555 nm
A) 50W done
clear
B) 72W done
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C) \[120\times {{(0.6)}^{2}}W\] done
clear
D) 200W done
clear
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question_answer40) Find the luminous intensity of the sun if it produces the same illuminance on the earth as produced by a bulb of 10000 candela at a distance 0.3 m. The distance between the sun and the earth is \[1.5\times {{10}^{11}}m\]
A) \[25\times {{10}^{22}}cd\] done
clear
B) \[25\times {{10}^{18}}cd\] done
clear
C) \[25\times {{10}^{26}}cd\] done
clear
D) \[25\times {{10}^{36}}cd\] done
clear
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question_answer41) A lamp is hanging at a height of 4m above a table. The lamp is lowered by 1m. The percentage increase in illuminace will be
A) 40 % done
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B) 64% done
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C) 78% done
clear
D) 92% done
clear
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