Electrical Power Engineering Multiple Choice Questions and Answers (MCQs) Part 7:

302. Sky appears blue due to

(a) radiation.
(b) reflection.
(c) refraction.
(d) scattering of light over dust particles.

Answer : (d) scattering of light over dust particles.

303. Colour of light depends upon

(a) velocity of light.
(b) frequency.
(c) wavelength.
(d) both (b) and (c).

Answer : (d) both (b) and (c).

304. The wave length of 5,500 Å will give light of

(a) green colour.
(b) red colour.
(c) orange colour.
(d) yellow-green colour.

Answer : (d) yellow-green colour.

305. Which of the following colour has wavelength between blue and yellow ?

(a) Violet.
(b) Orange.
(c) Red.
(d) Green.

Answer : (d) Green.

306. Luminous flux is

(a) the rate of energy radiation in the form of light waves.
(b) the part of light energy, radiated by Sun that is received on earth.
(c) measured in lux.

Answer : (a) the rate of energy radiation in the form of light waves.

307. Candle power is

(a) the luminous flux emitted by the source per unit solid angle.
(b) the light radiating capacity of a source in a given direction.
(c) the unit of illumination.

Answer : (b) the light radiating capacity of a source in a given direction.

308. Glare is caused due to

(a) excessive luminance.
(b) excessive lighting contrast in the field of vision.
(c) either (a) or (b).

Answer : (c) either (a) or (b).

309. A perfect diffuser surface is one that

(a) transmits all the incident light.
(b) absorbs all the incident light.
(c) diffuses all the incident light.
(d) all of the above.

Answer : (d) all of the above.

310. The illumination at a surface due to a source of light placed at a distance ‘d’ from the surface varies as

(a) 1/d2
(b) 1/d
(c) d
(d) d2

Answer : (a) 1/d2

311. The illumination at various points on a horizontal surface illumi­nated by the same source varies as

(a) cos θ
(b) cos2 θ
(c) cos3 θ
(d) 1/cos θ

Answer : (c) cos3 θ

312. Carbon arc lamps are commonly used in

(a) cinema projectors.
(b) domestic lighting.
(c) factory lighting.
(d) street lighting.

Answer : (a) cinema projectors.

313. Fine diameter tungsten wires are made by

(a) turning.
(b) wire drawing.
(c) swaging.
(d) compressing.

Answer : (b) wire drawing.

314. The melting point of tungsten is

(a) 3,400°C
(b) 2,800°C
(c) 2,600°C
(d) 2,400°C

Answer : (a) 3,400°C

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

(a) 10-2 mm Hg
(b) 10-4 mm Hg
(c) 10-6 mm Hg
(d) 10-8 mm Hg

Answer : (b) 10-4 mm Hg

316. The rate of evaporation of tungsten filament in a lamp depends upon

(a) exhaust tube diameter.
(b) glass shell diameter.
(c) vapour pressure inside.
(d) none of the above.

Answer : (c) vapour pressure inside.

317. Heat from the lamp filament is transmitted to the surrounding mainly through

(a) circulation.
(b) conduction.
(c) convection.
(d) radiation.

Answer : (d) radiation.

318. Which of the following material is most commonly used for the filaments in incandscent lamps ?

(a) Tungsten.
(b) Osmium.
(c) Tantalum.
(d) Silver.

Answer : (a) Tungsten.

319. A zero watt lamp consumes power of

(a) zero watt.
(b) 5-10 W.
(c) about 15 W.
(d) about 25 W.

Answer : (b) 5-10 W.

320. The safe operating temperature of a tungsten filament lamp is

(a) 1,000°C
(b) 2,000°C
(c) 3,000°C
(d) 3,500°C

Answer : (c) 3,000°C

321. The output of a tungsten filament depends on

(a) size of the shell.
(b) size of the lamp.
(c) temperature of filament.
(d) all of the above.

Answer : (c) temperature of filament.

322. What percentage of the input energy is radiated by filament lamps ?

(a) 60-70 per cent.
(b) 40-50 per cent.
(c) 25-30 per cent.
(d) 10-15 per cent.

Answer : (d) 10-15 per cent.

323. An electric bulb, when broken, produces bang. It is on account of

(a) vacuum inside the bulb.
(b) pressure inside is equal to that outside.
(c) pressure of air in the bulb.
(d) none of the above.

Answer : (a) vacuum inside the bulb.

324. In an incandescent lamp, bird cage filament is usually used in vacuum bulb so as to

(a) increase the life span of the filament.
(b) give uniform radiations.
(c) reduce the oxidation phenomenon.
(d) reduce the convection losses.

Answer : (b) give uniform radiations.

325. Filament lamps normally operate at a power factor of

(a) 0.5 lagging.
(b) 0.8 lagging.
(c) unity.
(d) 0.85 leading.

Answer : (c) unity.

326. Most affected parameter of a filament lamp due to variation in operating voltage is

(a) life.
(b) light output.
(c) luminous efficiency.
(d) wattage.

Answer : (a) life.

327. The lumens output of an incandescent lamp with the variation in operating voltage is given as lumens output α Vn where n is a constant. The value of n for tungsten is

(a) from 1.0 to 2.2
(b) from 3 to 4
(c) from 8 to 10
(d) from 10 to 12

Answer : (b) from 3 to 4

328. Which gas is sometimes used in filament lamps ?

(a) Nitrogen.
(b) Carbon dioxide.
(c) Argon.
(d) Krypton.

Answer : (c) Argon.

329. Which of the following vapour/gas will give yellow colour in a filament lamp ?

(a) Helium.
(b) Mercury.
(c) Magnesium.
(d) Sodium.

Answer : (d) Sodium.

330. Magnesium vapour in a filament lamp gives

(a) green colour light.
(b) pink colour light.
(c) blue colour light.
(d) white colour light.

Answer : (a) green colour light.

331. The gas used in a gas-filled filament lamp is

(a) helium.
(b) oxygen.
(c) nitrogen.
(d) ozone.

Answer : (c) nitrogen.

332. In filament lamps, coiled coil filaments are used in

(a) coloured lamps.
(b) gas-filled lamps.
(c) low wattage lamps.
(d) higher wattage lamps.

Answer : (b) gas-filled lamps.

333. In electric discharge lamps, light is produced by

(a) magnetic effect of current.
(b) heating effect of current.
(c) cathode ray emission.
(d) ionisation in a gas or vapour.

Answer : (d) ionisation in a gas or vapour.

334. In electric discharge lamps for stabilization of arc

(a) a choke is connected in series with the supply.
(b) a variable resistance is connected in series with the circuit.
(c) a condenser is connected across the supply.
(d) any of the above.

Answer : (a) a choke is connected in series with the supply.

335. Glow lamps

(a) have hot cathode.
(b) have cold cathode.
(c) draw more power.
(d) cannot withstand shocks.

Answer : (b) have cold cathode.

336. Halogen lamps have the advantage(s) of

(a) reduced dimensions of the lamp.
(b) better colour rendition and longer life (about 2,000 hours).
(c) high operating temperature with increased luminous efficiency.
(d) all of the above.

Answer : (d) all of the above.

337. The filament of a GLS lamp is made of

(a) aluminium.
(b) tungsten.
(c) carbon.
(d) copper.

Answer : (b) tungsten.

338. Which of the following is not the GLS lamp of the standard rating ?

(a) 15 W
(b) 40 W
(c) 75 W
(d) 100 W

Answer : (c) 75 W

339. The luminous efficiency of GLS lamps is normally in the range of ………….. lumens/watt.

(a) 100 to 150
(b) 75 to 100
(c) 50 to 75
(d) 10 to 18

Answer : (d) 10 to 18

340. Nitrogen or argon is filled in GLS lamps so as to

(a) retard evaporation of tungsten filament.
(b) improve efficiency.
(c) change the colour of the light.
(d) reduce the glare.

Answer : (a) retard evaporation of tungsten filament.

341. In case of frosted GLS lamps, frosting of shell is done by

(a) acid etching.
(b) ammonia.
(c) ozone.
(d) salt water.

Answer : (b) ammonia.

342. In case of GLS lamps the increase in supply voltage reduces

(a) power consumption.
(b) lumens output.
(c) life.
(d) efficiency.

Answer : (c) life.

343. Sodium vapour lamp needs an ionisation voltage of about

(a) 5 V
(b) 20 V
(c) 50 V
(d) 100 V

Answer : (a) 5 V

344. The ignition voltage for a sodium lamp is about

(a) 100-125 V
(b) 200-240 V
(c) 300-400 V
(d) 400-600 V

Answer : (d) 400-600 V

345. When a sodium vapour lamp is switched on, initially the colour is

(a) red.
(b) pink.
(c) yellow.
(d) blue.

Answer : (b) pink.

346. The colour of light given out by a sodium vapour discharge lamp is

(a) pink.
(b) bluish green.
(c) yellow.
(d) blue.

Answer : (c) yellow.

347. An auto-transformer used with a sodium vapour lamp should have

(a) high step-up ratio.
(b) high step-down ratio.
(c) high leakage reactance.
(d) high resistance.

Answer : (c) high leakage reactance.

348. Leak transformer in a sodium vapour lamp initially provides

(a) high current.
(b) low voltage.
(c) high voltage.

Answer : (c) high voltage.

349. In a sodium vapour discharge lamp the neon gas

(a) changes the colour of light.
(b) prevents vapourization of filament.
(c) acts as a shield around the filament.
(d) assists in developing enough heat to vapourize the sodium.

Answer : (d) assists in developing enough heat to vapourize the sodium.

350. The capacitor is used in auto-transformer circuit of a sodium vapour lamp in order to

(a) regulate discharge voltage.
(b) improve the circuit power factor.
(c) control lamp illumination level.
(d) protect the lamp against over-voltage.

Answer : (b) improve the circuit power factor.

351. The sodium vapour lamp

(a) is only suitable for ac and so needs choke control.
(b) needs capacitor in its auto-transformer circuit to improve the power factor which is very low (about 0.3 lagging).
(c) comes up to its rated output in approximately 15 minutes.
(d) all of the above.

Answer : (d) all of the above.