THE TRANSFORMER 



207 



wire and to one side of the line. The parallel resistance of the 

 two 5-ohm coils is 2.5 ohms, which being in series with ."> ohms 

 makes a total resistance of 7.5 ohms across the 100-volt circuit. 

 The total current flowing is 100/7.5 = 13.3 amp. This 13.3 

 amp. divides equally between the two parallel resistances, making 

 6.67 amp. in each. The voltage across the single 5-ohm 

 tanee is (J6.7 volts and that across the 5-ohm resistance which 

 constitutes the load is 33.3 volts. In 

 order to obtain 6.67 amp. at 33.3 

 volts with this system, the line must 

 supply 13.3 amp. at 100 volts. The 

 efficiency of this system is therefore 

 very low. - c -*-e.a 



ire 197 (a) shows a transformer FIG. 196. Currents in a drop- 



whose primary ac is connected across 



100-volt alternating-current supply. The secondary 6V has 

 ju<t half the number of turns of the primary ac, and therefore 

 the voltage across the secondary is 50 volts. This secon- 

 dary 6V supplies a 2. 5-ohm resistance so that the secondary 

 current is 20 amp. Instantaneous directions of currents are 

 indicated. NVirleeting the magnetizing current, the primary cur- 

 rent /. : . is 10 amp. flowing downwards as indicated. It will be 

 noted that the secondary current / C V is 20 amp. flowing upward*. 



O 10 Airp._^_ a 



2.6ft 



-- 10 Amp. o -*-jo Amp. 

 (6) Auto-traniformer 



*- 10 Amp? c ' *-20Amp. 

 (a) Regular Tranilorir.or 



197. Currents and volt.mos in an a i'lyiiik' 



per cent, voltage. 





If the secondary winding /- -mbined with the part he 



of the primary winding, where /; is the mid-point of the winding 

 in-, no disturbance will occur, a- the VOltag iMjual to the 



iinl the tw are >nb-tanlially in })ha>e. The cur- 

 rent fln\vs airain-t the emf. in \vinlinu / and with the emf. in 

 winding &V.) A time that the winding he and //' ate ii 

 tact point gi-. winding, as shown in Fig. 197 



