$A$ thermoelectric refrigerator works on

The negative feedback in an amplifier

In an oscillator,for sustained oscillations,the Barkhausen criterion is $A \beta$ equal to (where $A =$ voltage gain without feedback,$\beta =$ feedback factor).

If in a $p-n$ junction diode,a square input signal of $5 \ V$ to $-5 \ V$ is applied as shown,which of the following represents the output signal across $R_L$?

The amplifiers $X, Y$ and $Z$ are connected in series. If the voltage gains of $X, Y$ and $Z$ are $10, 20$ and $30$ respectively,and the input signal is $1 \, mV$ peak value,then what is the output signal voltage (peak value) $(i)$ if $DC$ supply voltage is $10 \, V$? $(ii)$ if $DC$ supply voltage is $5 \, V$?

In which of the following circuits is the junction reverse biased?