tand hook
switches of the Western Electric Company and of the Kellogg
Switchboard and Supply Company.

30. Give conventional symbols of hook switches.

REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 143--225

* * * * *

1. Describe an electromagnet and its function in telephony.

2. Sketch an iron-clad electromagnet.

3. What is a differential electromagnet? Sketch and describe one type.

4. State the desirable characteristics of good enamel insulation for
magnet wire.

5. If you have a coil of No. 23 double cotton B. and S. wire of 115
ohms resistance and you have to rewind it for 1,070 ohms resistance
with double cotton wire, what number of wire would you take? Show
calculation.

NOTE. No. 23 d. c wire has res. 1.772 ohms per cubic inch; for
the core, 115 ohms. There are required in the coil 1,070 ohms,
that is, 9.3 times as much. 1.772 x 9.3 = 16.47 ohms, which must
be the resistance per cu. in. This resistance gives, according to
Table IV, No. 29 wire.

6. What is an impedance coil? State how it differs from an
electromagnet coil.

7. Describe the different kinds of impedance coils.

8. Give symbol of impedance coil.

9. What are the principal parts of an induction coil?

10. What is the function of an induction coil in telephony?

11. What is a repeating coil and how does it differ from an induction
coil?

12. Give conventional symbols of induction coils and repeating coils.

13. Enumerate the different types of non-inductive resistance devices
and give a short description of each.

14. Define condenser.

15. What is the meaning of the word _dielectrics_?

16. State what you understand by the specific inductive capacity of a
dielectric.

17. Upon what factors does the capacity of a condenser depend?

18. What is the usual capacity of condensers in telephone practice?

19. Give conventional condenser symbols.

20. By what two methods may the current be supplied to a telephone
transmitter?

21. Make sketch of local-battery stations with metallic circuit.

22. Sketch common-battery circuit in series with two lines.

23. State the objections against the preceding arrangement.

24. Make sketch of the standard arrangement of the Western Electric
Company in bridging the common battery with repeating coils.

25. Sketch the arrangement of bridging the battery with impedance
coils and state the purpose of the coils.