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21. 

The transistor has a collector current of 2 mA. If the current gain is 135, what is the base current?
A. 14.8 µA
B. 10.3 µA
C. 7.8 µA
D. 7.75 µA
E. None of the above
22. 

Current and voltage are said to be in phase when:
A. their waveforms are both ac or both dc
B. they have the same amplitude and frequency
C. their waveforms cross through zero and reach positive and negative peaks at the same time
D. All of the above
E. None of the above
23. 

Silicon atoms combine into an orderly pattern called a
A. Crystal
B. Covalent bond
C. Semiconductor
D. Valence orbit
E. None of the above
24. 

The rotating coil of wire in an electric motor is called the:
A. armature
B. brush
C. commutator
D. loop
E. None of the above
25. 

The north pole of a magnet is the one:
A. that has its molecules arranged in a random pattern
B. that would be attracted to the earth's north magnetic pole
C. that would be repelled by the south pole of another magnet
D. that would be attracted to the earth's south magnetic pole
E. None of the above