illustrated, ringing and listening
keys are provided instead of the jack-and-plug arrangement of the wall
type. In this case also, the top section carries an arm for supporting
a swinging transmitter instead of the hook support for the combined
transmitter and receiver.

REVIEW QUESTIONS

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REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 11--62

* * * * *

1. When was the telephone invented and by whom?

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 spacing of poles?

11. State the four principal 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 telep