Electric Illumination MCQs

76. Which of the following filament material has the lowest melting point?

(A) Carbon
(B) Tungsten
(C) Tantalum
(D) Osmium.

Answer
Answer. D

77. The operating characteristics of an incandescent lamp arc materially affected by departure from its normal operating voltage. The total number of lumens given out by the lamp increases with the increase in operating voltage and the relation between them is: 

Lumens output α Vn

where n is a constant. The value of n for tungsten varies for

(A) 0.5 to 0.75
(B) 1.5 to 2.5
(C) 4 to 5
(D) 8 to 10.

Answer
Answer. C

78. Filament lamps operate normally at a power factor of

(A) 0.5 leading
(B) 0.5 lagging
(C) unity
(D) 0.8 lagging.

Answer
Answer. C

79. Neon gas in sodium vapor lamp

(A) changes the color of light
(B) acts as a shield around the filament
(C) assists in developing enough heat to vaporize the sodium
(D) prevents vaporization of filament.

Answer
Answer. C

80. Which of the following is a cold cathode lamps?

(A) Sodium vapor lamp
(B) High pressure mercury vapor lamp
(C) Low pressure mercury vapor lamp
(D) Neon lamp.

Answer
Answer. D

81. In fluorescent tubes ballast resistance is connected in series with the choke

(A) when supply frequency is low
(B) to reduce radio interference
(C) when tube operates on dc supply
(D) to reduce stroboscope effects.

Answer
Answer. C

82. While comparing tungsten filament lamps with fluorescent tubes, all of the following are the advantages in favor of tungsten filament lamp EXCEPT

(A) Longer life
(B) Less costly
(C) More brightness
(D) Simple installation.

Answer
Answer. A

Questions 83 to 85 refer to data given below:

The 220 V lamps, one of 60 W and the other of 75 W are connected in series across a 440 V supply.

83. The potential difference across 60 W lamp will be

(A) 195 V
(B) 220 V
(C) 245 V
(D) 440 V.

Answer
Answer. C

84. The potential difference across 75 watt lamp will be

(A) 195 V
(B) 220 V
(C) 245 V
(D) 440 V

Answer
Answer. A

85. Assuming candle power to be proportional to fourth power of the voltage, the candle power of 60 W lamps under above conditions as a percentage of its value under normal operation at 220 V will be

(A) 110%
(B) 1549%
(C) 220%
(D) 440%.

Answer
Answer. B

Questions 86 to 88 refer to data given below:

A 60 CP 250 V metal filament lamp has a measured candle power of 17.5 CP at 260 V and 50 C.P. at 240 V.

86. If the equation for C and V is C = aVwhere C = candle power and V = voltage, the value of constant b is

(A) 4.5
(B) 0.98 x l0-9
(C) 0.98 x 10-6
(D) 450.

Answer
Answer. A

87. The value of constant is a

(A) 0.98 x 10-9
(B) 0.98 x 10-7
(C) 0.98 x 10-5
(D) 0.98 x 10-3.

Answer
Answer. A

88. The change in candle power per volt at 250 V will be

(A) 1.1 V
(B) 4.4 V
(C) 8.8 V
(D) 17.6 V.

Answer
Answer. B

Questions 89 to 90 refer to data given below:

A 110 V lamp 16 C.P. and a lamp of the same material and worked at the same efficiency develops 25 CP on 220 V.

89. The ratio of diameters of the filaments will be

(A) 0.54
(B) 1.0
(C) 1.18
(D) 1.78.

Answer
Answer. C

90. The ratio of lengths of the filaments will be

(A) 0.54
(B) 1.0
(C) 1.18
(D) 1.78.

Answer
Answer. A

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