21. What does mho denote?
22. Why are Pupin's coils not so successful on open wires?
23. What is a repeater?
24. Define reactive interference.
25. State the frequencies of the pitches of the human voice.
26. What is the office of a diaphragm in a telephone apparatus?
27. What transmitter material has greatly increased the ranges of speech?
28. Describe the different methods of measurements of telephone circuits.
29. What are the two kinds of electric calls?
30. How many conductors has a telephone line?