The figure shows an intrinsic semiconductor $S$ connected in series with a variable resistor $R$ and a constant voltage source $V$. The value of $R$ can be adjusted to maintain a constant current in the ammeter $A$. Under what condition will the semiconductor $S$ get heated? Give reasons.

In an oscillator,if $\beta$ is the feedback factor and $A$ is the gain of the amplifier,then sustained oscillations are obtained when:

Which of the following is used to produce radio waves of constant amplitude?

The voltage gain of the following amplifier is

Arvind needs to identify the electrical components from a group of components labelled as $A, B, C$ and $D$. He performed some simple tests and obtained the following observations:
$(a)$ $A$ has a silver ring at one end,with two terminals. It conducts electricity only in one direction.
$(b)$ $B$ is connected to a $D.C.$ source,but the current gradually decreases and becomes zero. It is a two-terminal device and behaves the same in both directions.
$(c)$ $C$ is a two-terminal device,which conducts electricity only in one direction,while emitting light.
$(d)$ $D$ is a two-terminal device with several coloured rings on it. It conducts current in both directions with the same steady current.
The correct identification of $A, B, C$ and $D$ are respectively:

Two amplifiers are connected one after the other in series (cascade). The first amplifier has a voltage gain of $10$ and the second has a voltage gain of $20$. If the input signal is $0.01\, V$,the output $ac$ signal will be........$V$.