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.

26.  Make diagram of a common-source current supply for many lines with repeating coils and point out the travel of the voice currents.

27.  Name the different parts which comprise a telephone set.

28.  What is a magneto telephone?

29.  Make diagram of the circuit of a series magneto set with receiver on the hook and explain how the different currents are flowing.

30.  Show diagram of the Stromberg-Carlson magneto desk telephone circuit and describe its working.

31.  Give sketch of the Stromberg-Carlson common-battery wall set circuit.