My speciality. Овчинникова Т.Е - 9 стр.

      2 Section 2

      2.1 Part 1

      2.1.1 Mind the pronunciation of these words, remember them

constant, increase n, decrease n, observe, value, evidently, limitation, potential,
surrounding, velocity, overcome, extremely, vary, increase v, decrease v, cathode,
thereby, presence, toward, urge, eventually, constitute, sufficient, range, precisely,
characteristic, rare, resistance, nevertheless, concept, quantity, ratio, diode,
neighborhood, pulse , approximately, succession, unidirectional.

       2.1.2 Find 2 conditional sentences in paragraph 2 and define their types
       State the function of the infinitive to obtain in paragraph 6

                                 SPACE CHARGE

1. If the plate potential is held constant at E b1 and the heater current I f is
varied, the lower curve of Figure 1 is obtained. On increasing the plate voltage
to a higher value Eb 2 it is observed that the plate current is increased, but
only at the higher cathode temperatures (larger values of I f ). Evidently
temperature saturation is responsible for the agreement of the two curves in
the lower region. Both curves are known to be nearly horizontal in the upper
part, and this limitation of current is caused by the presence of a space charge
near the cathode.
2. As electrons are given off by the cathode, they form a cloud of negative
charges in the surrounding space. These negative charges lower the potential
in that region, and thereby produce a field which ugres the electrons back
toward the cathode. If there were no plate, all the electrons emitted would
eventually return to the cathode. Even with the plate at a positive potential,
only the electrons emitted with the sufficient velocity will have enough energy
to penetrate the cloud, and their motion will constitute the plate current. If the
plate voltage is increased, it will further overcome the effect of space charge,
and thereby produce an increase of plate current.
3. This effect of space-charge limitation is extremely important , as the useful
working range of nearly all vacuum tubes is precisely the region in which a
mission is limited by temperature saturation are very rare.
4. Although the relationship between plate current and plate voltage is not one
of simple proportion and cannot be expressed in terms of Ohm’s Law, one may
nevertheless speak of the resistance of the internal plate circuit of the tube.
The ratio of plate potential to plate current is known as the direct current plate
resistance, and is show in Figure 2 as OA/AP. concept of D.C. plate resistance is
useful in many cases where the current through the tube is steady or constant, but a
much more important quantity is the alternating current plate resistance, or the ratio
of change in plate voltage to change in plate current. In yhe neighbourhood of point P