76. Which of the following filament material has the lowest melting point?
(A) Carbon
(B) Tungsten
(C) Tantalum
(D) Osmium.
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.
78. Filament lamps operate normally at a power factor of
(A) 0.5 leading
(B) 0.5 lagging
(C) unity
(D) 0.8 lagging.
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.
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.
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.
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.
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.
84. The potential difference across 75 watt lamp will be
(A) 195 V
(B) 220 V
(C) 245 V
(D) 440 V
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%.
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 = aVb where 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.
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.
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.
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.
90. The ratio of lengths of the filaments will be
(A) 0.54
(B) 1.0
(C) 1.18
(D) 1.78.
