CHAPTER 6
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HIGH VACUUM, LOW—VOLTAGE TUBES
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6—1.
Space Charges.—lf the voltage on the plate of a diode
is comparatively small, the observed current Will be less than that
given by Richardson’s equation, as indicated by the dotted portion
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of the curve 071 in gure 5—5. This is due to the repellent action
of electrons in the region between the lament and plate on the
outcoming electrons. The electrons in transit, repel other electrons
'
which are behind them and may even drive them back into the
filament.
Thus a cloud of electrons forms “in the space between
the lament and plate, With
charge density near the
'
lament.
Although electrons are continuallyf entering and leav—
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ing this space
its density at a given point remains essentiàlly Constant if“ the voltage and
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PLATE
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temperature remain
constant.
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