472 ALTERNATING CURRENTS 



found in( a), be at 440 volts? (d) How does the kv-a. capacity of a con- 

 denser vary with the voltage? 



26. A certain condenser when connected across 115-volt 25-cycle alter- 

 nating-current mains takes 8 amp. What current does it take if the frequency 

 and capacitance are both doubled? 



27. Repeat problem 26 for an inductance taking 8 amp. under the same 

 conditions. 



28. In a circuit having an inductive reactance of 8 ohms and an ohmic 

 resistance of 6 ohms, 12 amp. flow, (a) What is the voltage across the 

 resistance? (b) Across the reactance? (c) What is the circuit voltage? 



(d) How much power does the circuit take and what is its power-factor? 



(e) What is the phase angle between the circuit voltage and the current? 



29. What is the power-factor of a circuit which has a resistance of 3 ohms 

 and a reactance of 4 ohms? What current flows if the voltage is 60 volts 

 and how much power does the circuit consume? 



30. Repeat problem 29 making the inductive reactance twice the value 

 given. 



31. What current flows in a circuit consisting of a 40 m.f. condenser and 

 30 ohms resistance in series if connected across 120-volt 60-cycle mains? 

 What is the voltage across the resistance? The condenser? What power 

 does the circuit take and what is its power-factor? 



32. Repeat problem 31 substituting a 50 m.f. condenser for the 40 m.f. 

 condenser. 



33. A series circuit consisting of 10 ohms resistance, 15 ohms inductive 

 reactance, and 20 ohms condensive reactance is connected across 220- volt 

 60-cycle mains. Find (a) the current, (b) The voltage across each circuit 

 member, (c) The power taken by the circuit, (d) The power-factor and 

 power-factor angle of the circuit. Draw a vector diagram of the circuit 

 to scale. 



34. A potential difference of 220 volts at 60 cycles is impressed across a 

 circuit having 50 ohms resistance, 15 m.f. capacitance and 0.2 henry induc- 

 tance all in series, (a) What current flows? (6) What is the voltage 

 across the resistance, the inductance and the capacitance? (c) What power 

 does the circuit consume? (d) What is its power-factor and power-factor 

 angle? Draw a vector diagram of this circuit to scale. 



35. A resistance of 10 ohms, an inductance of 0.1 henry and a 40 m.f. 

 condenser are connected in series across 220- volt 60-cycle mains, (a) What 

 current flows? (6) What power is taken from the line? (c) What is the 

 voltage across the resistance, the inductance and the capacitance? (d) 

 What is the circuit power-factor and power-factor angle? Draw a vector 

 diagram. 



36. If the inductance of problem 35 were adjustable, for what value would 

 the current be a maximum? Find the current, the power, the power-factor 

 and the voltages under these conditions. 



37. A circuit contains a resistance of 10 ohms and an inductance of 0.352 

 henry and a variable condenser all in series. If the frequency is 60 cycles, 



