QUESTIONS AND PROBLEMS :, 1 I 



172. A multiple. direct-current, ll.">-vilt. enclosed arc takes 550 watts at 

 115 volts and has a mean spherical candlepower of 165. (a) What is 

 the efficiency in watts per mean spherical candlepower? (6) In lumens 



173. A series, din ( t -current, 6.6-amp., enclosed arc lamp requires 

 itts and has a mean spherical candlepower of 270. (a) What is ite 



rating in watts per mean spherical candlepower? (6) In lumens }x>r watt? 

 Compare this efficiency with that of the arc lamp of problem 172. which is 

 similar. Account for the difTerei, 



174. A series, alternating-current, 6.6-amp., enclosed-carbon, arc lamp 

 130 watts at a power-factor of 0.85, and gives a mean s andle- 



of !:;:>. The arc itself takes 420 watts, and the arc -ml the 



arc voltage are substantially in phase with each other, (a) What i> the 

 effiriency of the entire lamp in watts per mean spherical candlepower? 

 (6) In lumens per watt? (c) What is the voltage across the arc? (d) Draw 

 to scale a vector diagram, (e) Why is the power-factor of this lamp less 

 than unity? 



175. A multiple alternating-current arc which takes 0.54 amp. at 115 

 volts and a power-factor of 0.70, has a mean spherical candlepower 



of this lamp in watts per mean spherical candle- 

 power? (6) In lumens per watt? (c) The voltage across the arc 

 volts and is substantially in phase with the current. Draw a vector diagram 

 of this arc. (d) How much power is consumed by the auxiliary <]. 

 (e) Compare this jxnver with similar j>ower consumed in the direct-current, 

 multiple arc lamp. (See problems 170, 171 and 172.) 



176. A series magnetite lamp takes 6.6 amp. at 75 volts and has a rating 

 of 550 m.s.cp. What is the efficiency in watts per mean spherical candle- 

 power? Lumens per watt? 



177. Assume that a lamp similar to that of problem 17G is arranged to 

 go in multiple across 110-volt direct-current mains, and that the arc itself 

 takes the same volts and the same watt* and ha* the same candle-power. 

 What is the over-all light efficiency of this lamp in lumens per \\ 



178. A lamp trimmer receiving $8 trim 75-500-watt magne- 

 tic- lamps in that time. Allowing 1.1 Bfe per kilowatt i 



120 burning hours JXT trim. 10 cts. per electrode and $51.00 pei 

 maintenance, compute tl -ating cost per year of such a 



lamp assuming that a lamp i > 4. (KM) hr. (luring tl 



179. In a photometric r . nt the standard lamp has a candlepower 

 rid the photometric balance is obtained \\hen ti 



is 10 m. from the standa; nd SO in. from the tost lamp. V 



the candle|K>wer of the test lamp'.' 



180. Compute the candle|x>v 'her test lamp in problem 179 when 



i< 20 m from the standard lamp. The distance betwe. 



181. The test lamp in problem 179 has a aph- n factor of 

 0.82. it* mean spherical candlepower and what u> iU output in 

 lumens? 



