Electric Illumination MCQs

46. The frequency of flickers in a fluorescent lamp at 220 V, 50 Hz supply will be

(A) 25 per second
(B) 50 per second
(C) 100 per second
(D) 220 per second.

Answer. C

47. Wavelength of green color is nearly

(A) 4000 A
(B) 4500 A
(C) 5000 A
(D) 5500 A

Answer. D

48. One Angstrom is

(A) 10-6 meter
(B)10-8 meter
(C) 10-8 cm
(D) 10-8 mm.

Answer. C

49. Which of the following color has wavelength between green and colour?

(A) Yellow
(B) Blue
(C) Violet
(D) None.

Answer. A

50. The purpose of providing a choke in a tube light is

(A) to eliminate corona effects
(B) to avoid radio interference
(C) to improve power factor
(D) to limit current to appropriate value.

Answer. D

51. A 60 W lamp given a luminous flux of 1500 lumen. Its efficiency is

(A) 1500 lumen/watt
(B) 250 lumen/watt
(C) 25 lumen/watt
(D) 2.5 lumen/watt.

Answer. C

52. One lux is the same as

(A) one lumen/sq. cm
(B) one lumen/sq. m
(C) one lumen/100 sq. m
(D) one lumen/1000 sq. m.

Answer. B

53. The vacuum inside an incandescent lamp is of the order of

(A) 10-2 mm Hg
(B) 10-3 mm Hg
(C) 10-4 mm Hg
(D) 10-5 mm Hg.

Answer. C

54. Which of the following application does not need ultra-violet lamps?

(A) Medical purposes
(B) Aircraft cockpit dashboard lighting
(C) Car lighting
(D) Blue print machines.

Answer. C

55. When using ultra-violet lamps the reflector for maximum should be made of

(A) aluminium
(B) copper
(C) leaf
(D) glass

Answer. A

56. Which of the following combination of gas is filled in lamp and the resulting color is incorrect?

(A) Neon-red
(B) Nitrogen-buff
(C) Carbon dioxide – day light white
(D) Magnesium-white.

Answer. D

57. Which of the, following vapors/gas will give yellow color in a filament lamp?

(A) Helium
(B) Mercury
(C) Sodium
(D) Magnesium.

Answer. C

58. Which of the following phosphor produces green color

(A) Zinc silicate
(B) Cadmium borate
(C) Magnesium tungstate
(D) Calcium halo phosphate.

Answer. A

59. If d is the distance of a surface from a source, the illumination of the surface will vary as

(A) d
(B) 2d
(D) 1/ d 2

Answer. D

60. The level of illumination on surface least depends on

(A) candle power of the source
(B) distance of the source
(C) type of reflector used
(D) ambient temperature.

Answer. D

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