PROBLEMS. 399 



total primary current. Resistance of secondary coil is to be 

 neglected. 



102. A transformer has 1,300 turns of wire in its primary coil 

 and 130 turns in its secondary coil. The primary coil takes 

 current from i,ioo-volt mains and the secondary coil delivers 200 

 amperes to a receiving circuit of which the power factor is 0.85. 

 What is the equivalent primary resistance and reactance of the sec- 

 ondary receiving circuit ? Ans. r = 46.75 ohms, x = 28.98 ohms. 



103. A 10 : i transformer has its primary coil connected to 

 i,ioo-volt mains through a non-inductive resistance of 200 ohms 

 and its secondary arranged to deliver current to a non-inductive 

 resistance of 3 ohms. Find : (a) the resistance of a simple circuit 

 which is equivalent to the whole arrangement here specified ; (&) 

 the current delivered to the primary circuit of the transformer ; 

 (c) the secondary current ; (</) the secondary terminal voltage ; 

 (e) primary terminal voltage. Ans. (a) 500 ohms, (fr) 2.2 

 amperes, (c) 22 amperes, (d) 66 volts, (e) 660 volts. 



104. The transformer specified in problem 103 is connected as 

 specified, with the exception that the secondary receiving circuit 

 has a reactance of 3 ohms and a negligible resistance. Find (a) 

 the resistance and reactance of the simple circuit which is equiva- 

 lent to the whole arrangement ; (b) the primary current ; (c) the 

 secondary current ; (d) the secondary terminal voltage ; and (e) 

 the primary terminal voltage. Draw a clock diagram showing 

 the phase relations of the various electromotive forces and cur- 

 rents. Ans. (d) 200 ohms resistance and 300 ohms reactance, 

 (b) 3.05 amperes, (c) 30.5 amperes, (d) 91.5 volts, (e) 915 volts. 



105. A transformer has its primary in two sections which can 

 be thrown in series or in parallel at will. This primary takes 

 current through a rheostat of resistance R f , and the secondary 

 supplies current to a non-inductive receiving circuit of resistance 

 R". Find the relation between R', R n ', N r (total), and N" 

 for which the secondary current is the same whether the primary 

 coils are in series or in parallel. Ans. R' = %(N' /N")*R". 



106. A bundle of iron wires of which the total sectional area is 



