2. State the velocity of sound in air. Is it higher in air than in a denser medium?

3. State and define the characteristics of sound.

4. Make sketch of Bell's original magneto telephone without permanent magnets.

5. Describe and sketch Hughes' microphone.

6. Which is, at present, the best material for varying the resistance in transmitters?

7. Give the fundamental differences between the magneto transmitter and the carbon transmitter.

8. What is the function of the induction coil in the telephone circuit?

9. Describe and sketch the different kinds of visible signals.

10. What should be the diameter of hard drawn copper wire in order to allow economical s.p.a.cing of poles?

11. State the four princ.i.p.al properties of a telephone line.

12. If in testing a line the capacity is changed what are the results found on the receiver and transmitter end?

13. Why is paper used as an insulator of telephone cables?

14. How does a conductor behave in connection with direct current and how with alternating current?

15. What influence has inductance on the telephone?

16. Define impedance and give the formula for it.

17. What is the usual specification for insulation of resistance in telephone cables?

18. If 750 feet of cable have an insulation resistance of 9,135 megohms, how great is the insulation resistance for 7 miles and 1,744 feet of cable?

19. What is the practical limiting conversation distance for No. 10 B.

and S. wire?

20. Describe Professor Pupin's method of inserting inductance into the telephone line.

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?

31. Give formula for capacity reactance and the meaning of the symbols.

32. Which American cities are joined by underground lines at present?

33. State the two practical ways of improving telephone transmission.

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 63--141

1. On what general principle are most of the telephone transmitters of today constructed?

2. Make sketch of the new Western Electric transmitter and describe its working.

3. Make sketch and describe the Kellogg transmitter.

4. What troubles were encountered in the earlier forms of granular carbon transmitters and how were they overcome?

5. What limits the current-carrying capacity of the transmitter? How may this capacity be increased?

6. State in what kind of transmitters a maximum degree of sensitiveness is desirable.

7. Show the conventional symbols for transmitters.

8. Describe a telephone receiver.

9. Sketch a Western Electric receiver and point out its deficiencies.

10. Make a diagram of the Kellogg receiver.

11. Describe the direct-current receiver of the Automatic Electric Company.

12. Describe and sketch the Dean receiver.