Note that for nearly all materials the current - voltage relation is
temperature dependent. Thus at low temperatures the curve in Fig.
(a) rises more steeply for positive V than at higher
temperatures, and at successively higher temperatures the asymmetry in
the curve becomes less and less pronounced.
The current - voltage
relation for a source may also be represented graphically. For a source
represented by Vab=E−Ir, that is, V=E−Ir, The graph appears
in Figure (b). The intercept on the V−axis, corresponding to
the open circuit condition (I=0), is at V=E, and the intercept
on the I−axis, corresponding to a short-circuit situation (V=0),
is at I=Er.
This relation may be used to find the
current in a circuit containing a non linear device, as in fig (c).
Its current voltage relation is shown in fig (d) and terminal
voltage V=E−Ir is also plotted on this graph, each curve represents a
current-voltage relation that must be satisfied, so the intersection
represents the only possible values of V and I. This amounts to a
graphical solution of two simultaneous equation of V and I,
one of which is nonlinear.
When a device has a nonlinear
voltage-current relation, the quantity VI is not constant.
This ratio may still be called resistance, but now it varies with
current; it is constant only for a device obeying Ohm's law. Often a
more useful quantity is dVdI, which expresses the relation
between a small change in current and the resulting voltage change.
This is called dynamic or incremental resistance. Which of the following vacuum tube devices shows negative resistance?
Note that for nearly all materials the current - voltage relation is
temperature dependent. Thus at low temperatures the curve in Fig.
(a) rises more steeply for positive V than at higher
temperatures, and at successively higher temperatures the asymmetry in
the curve becomes less and less pronounced.
The current - voltage
relation for a source may also be represented graphically. For a source
represented by Vab=E−Ir, that is, V=E−Ir, The graph appears
in Figure (b). The intercept on the V−axis, corresponding to
the open circuit condition (I=0), is at V=E, and the intercept
on the I−axis, corresponding to a short-circuit situation (V=0),
is at I=Er.
This relation may be used to find the
current in a circuit containing a non linear device, as in fig (c).
Its current voltage relation is shown in fig (d) and terminal
voltage V=E−Ir is also plotted on this graph, each curve represents a
current-voltage relation that must be satisfied, so the intersection
represents the only possible values of V and I. This amounts to a
graphical solution of two simultaneous equation of V and I,
one of which is nonlinear.
When a device has a nonlinear
voltage-current relation, the quantity VI is not constant.
This ratio may still be called resistance, but now it varies with
current; it is constant only for a device obeying Ohm's law. Often a
more useful quantity is dVdI, which expresses the relation
between a small change in current and the resulting voltage change.
This is called dynamic or incremental resistance. Which of the following vacuum tube devices shows negative resistance?
The correct option is C Tetrode
In the given vacuum tube devices except tetrode the plate current increases with increase in plate voltage. In tetrode the emission of secondary electrons occurs from the plate material itself. As the secondary electrons flow in opposite direction to that of plate current hence, the plate current reduces with increasing plate potential. Due to this the characteristics curve shows a dip(portion bc as shown in figure) in current, known as negative resistance region. Here, the slope of curve is
slope=IV⇒R∝IV
This means current decreases with increase in potential.
In the given vacuum tube devices except tetrode the plate current increases with increase in plate voltage. In tetrode the emission of secondary electrons occurs from the plate material itself. As the secondary electrons flow in opposite direction to that of plate current hence, the plate current reduces with increasing plate potential. Due to this the characteristics curve shows a dip(portion bc as shown in figure) in current, known as negative resistance region. Here, the slope of curve is
slope=IV⇒R∝IV
This means current decreases with increase in potential.
