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Table of
Contents. • U.S. Government Printing Office; 1945 - 618779
Chapter 19 QUIZ
VACUUM TUBES
1. In thermionic emission, why do electrons shoot off the metal surface?
2. Why is the air removed from a vacuum tube?
3. Why is the cathode negative regardless of battery connection?
4. Why does current never flow from plate to cathode?
5. How does a diode act as a rectifier?
6. How does the grid control current in a triode?
7. Why must the grid be biased negatively?
8. How does a triode amplify signals?
Chapter 19 ANSWERS
VACUUM TUBES
1. The heat increases the electrons speed so that
proton attraction can no longer hold them.
2. The air molecules would clog up the space around the
cathode. They would interfere with
the emission of electrons.
3. The space charge of electrons determine the cathode
polarity. Electrons are negative so
the cathode is negative.
4. Because the plate has no electrons emitted to make
up a current from plate to cathode.
5. The diode only passes current from cathode to plate.
When the plate is negative no
current can flow. Therefore,
only the current in the cathode to plate direction is passed.
6. The grid acts as a valve between cathode and plate.
The negativeness of the grid
controls the amount of current
that can pass to the plate.
7. The grid would lose control if it became positive.
Therefore, a negative bias prevents the
grid ever becoming
positive and losing control.
8. The cathode to plate current is strong. But this current
is controlled by very small charges
in grid potential.
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Chapter 19 |
